no.. it's not the age.  You will see people on this site with issues from infant SK to elderly.. it is situational.

It's all about the family dynamics of the home/life before we SMs entered the picture. I met DH when his kids were 27, 25, 23, 14 and 12. A mix of ages. The BM had mental issues which environmentally impacted some of the kids and two for sure, maybe 3 have some of her disorders by genetics. Add in PAS, along with lies and strategies to keep younger kids from DH...just a darn mess.

I will say this...I have found the hardest battles with the adult SKs though. For some reason, I can rationalize "bad" behavior in younger kids, knowing  they are being impacted by a mean/crazy BM. But adults?? These SHOULD know better. And most do but just continue on as BM's soldiers in her war. 

I agree that the ages don't have a lot to do with it. It's more the overall dynamic that you walked into.

SS18 was 10 when we got together. He loved me until his mom found out about me. Then it was all down hill from there. My situation there has been referred to as one of the worst on this site. 

SS23 was 15. Never had an issue. BM1 is out of the picture for the most part, lost all custody and visitation rights. She pops up every once in a while but she isn't local and isn't actually a problem. More.... entertainment for the evening. 

My kids were 9 and 7, 17 and 15 now. They have an ok relationship with DH. They know they can count on him and that he cares for him but they keep him at an arms distance. I think it is due to loyalty to their dad but that is another can of worms. 

It probably has more to do with how a SP perceives their SK than whether the SK behaves or not. Some people are great with kids and understand what is age-appropriate behavior. Other people are not and either have to learn or need to not be around kids.

Age can also impact the type of relationship that SKs have with their SP, and vice versa. SPs who come into the picture when SKs are younger are more likely to have a parental relationship, whereas coming in when they are a teen or young adult may just result in the SP being their parent's spouse with more of an in-law connection. Your mileage may vary on this given many other factors.

Really, age isn't a hard and fast rule for anything. It's a factor like everything else. A parented 4 year old can be more mature and well behaved than a non-parented 14 year old. And differences in how SKs behave can vary greatly even when they have the same parents. I've been seeing the phrase "you're a different parent with every kid" or something similar and I think that's very true. How my OSS was raised and how my YSK is being raised is quite different and has resulted in different outcomes. Same parents but different inputs.

Both my SKs are respectful to me (or at least do to my face) because my DH makes them be respectful. They were 11 and 7 when I came in the picture and their ages didn't seem to matter. DH's parenting, however, did.

In my case, it wasn't the ages of my SKs. It was a chicken-shit DH who wouldn't address anything. The SKs were feral and did their BM's dirty work for her and DH was way too chicken to address the kids on anything at all or they might not want to see Dad anymore. DH wouldn't so much as tell them to chew with their mouths closed or stop picking their noses let alone address the major manipulations and relational aggression they pulled. Since the brats were never addressed, they just didn't grow up to be very healthy people. 

SD was 5 or 6 when me and DH got together, she was excited to have me join the family at first, because I was a FUN person. I was always trying to be supportive and caring and I was NEVER trying to take BM's place. SD told me that BM told her she didn't want her calling me "Mom" (which I never even suggested) I told that she didn't have to call me "mom" she could call me ANYTHING she wanted. I told SD that it was totally OK to love her mom and dad the same, and it was ok to love me differently. I was supportive of EVERYONE, trying to make sure that SD never felt she had to betray ANYONE.

But regardless, SD was MEAN, HATEFUL, MANIPULATIVE, DESTRUCTIVE, LYING, NARCISSISTIC person who was ALWAYS trying to get my children into trouble, would literally intentionally create scenarios to get them into trouble. So no, the stress of being a SM had nothing to do with her age, but everything to do with who she was, her personality is 100% her mom's. it's EXACTLY who BM is.

Definitely nothing to do with age. SD was 3 and SS5. My case it's to do with a HCBM and a DH who over the course of our relationship/marriage developed a backbone to keep her and the skids in check. 

In my situation age made a HUGE difference.

I married my wife when my SDs were 13, 10, 7, 6 and while there were small issues here and there I got along and had a good relationship with each of them. 

I had an ex-husband who was angry with his ex-wife for leaving him (despite his cheating, hmm) and even had an argument with the oldest that caused him to leave for three years. His entire family was supportive of him doing this and the girls went through abandonment issues growing up. I wished I was a bit older and handled this situation better than I did.

Up until 18, every single one of those girls was well-behaved, got excellent grades, and worked a job. However when you have a whole side of a family that outright encourages rebellion against their mother and you then once they reach the age the government tells them they are an adult they take off and say horrible things about you and everyone else in order to get their dad's approval.

I have one SD who wishes me happy birthday, comes and visits whenever she can, and loves her half brothers and sisters. She is just a great person, but the others I only put up with for the sake of my wife. I do love them, but my relationship is estranged and I have moved on to greener pastures.

Met when I was 29 (3 years post divorce no kids). DW was 18.  My last year of 11yrs in undergrad.  DW's first year of university.  SD was 15mos old.  She had him at 16 and was never married to the Spermidiot.  She left SpermLand for university and never looked back.
 

We married the week before SS-30 turned 2yo.

Still married.  28+ years and counting.

Raised SS together.  Battled the SpermClan together.

We are proud of the man we raised.  He asked me to adopt him when he was 22.  We made that happen.

No major SKid issues.  Just the usual teen boy brain farts.

In my case, when DH and i got together the SD's were 6,8, and 10. The oldest one was standoffish at first, and then became very obstinant - refusing to eat what I cooked, refusing to do chores, refusing to clean up after herself, acting like she smelled something bad when I gave her a gift. She is still a problem - I think the PAS hit her the worst. The other two are having issues too, but those seem to be related to mental illness, or bad parenting - not as much of the PAS, but still it did influence them. 

I think the oldest had the most time with her family whole, and therefore didn't want to see me in a positive light - just as an intruder. 

My situation wasn't about my ex-SS's age, it was directly caused by sh&tty parenting.  His dad and mom babied him, set no expectations or consequences, went to great lengths to ensure he got whatever he wanted and never had to do anything he didn't want to do, including work...etc.  I left the situation for a number of reasons, my SS's behavior and failure to launch being the main one. 

I think how skids treat their stepparents is related more to how the parents raise the kid as opposed to age.  I also thinks it makes a difference how the parents view the stepparent and how they expect the skid to treat the stepparent.  My ex never taught his son to respect me either as my ex didn't respect me, so his son learned he could treat me poorly and get away with it.

In my experience it's not about age but about how the bio parents have taught the kid to treat people in general.  I was 18 when my dad remarried, 16 when he started dating my step mom.  It never occurred to me to treat her any way but with respect and kindness.  Both parents raised me to respect my elders and to be polite to people in general.  Had I deviated from that and treated her or anyone else rudely then I would've gotten in trouble with my dad first, then my mom would've dealt with me when I got home.  It didn't matter who it was.  Even if my mom had hated my step mom with the fury of a thousand suns she wouldn't have tolerated me being rude or disrespectful to her because she and Dad raised me better than that.  

SS was very young when I came into the picture.  While he was disrespectful to BM, SIL, and MIL, he was respectful to me.  I didn't tolerate any less than that.  Neither did DH and BM.  BM herself gave me the ok to deal with him if I needed to but I did try to have DH handle the discipline if he was present.  I felt it was their job to do so but I handled it when I needed to.  He learned early on that it was in his best interest not to cross me.  The difference I see in a lot of posts here is that the bio parents don't expect the kid to treat the step parent with respect.  SS was expected to treat me with respect by both bio parents.  Looking back now he probably thought I was just mean, but I had to be tough on him or he would have run over me like he did his mother, aunt, and grandmother.  I wasn't about to tolerate it.  As long as he was living under my roof he was going to respect me and if he didn't like it he could leave. And if DH didn't like it, well, too bad, keep your kid in line or we won't be together.  

We're estranged from SS now and have been for a few years. I'd say it was our choice but it may have been mutual between me and him; husband chose to stop talking to him because of how he was acting towards me.  It had nothing to do with BM as he pretty much cut her out of his lufe.