There's a 13 year age gap between my younger brother and me. My parents had me, my sister and older brother in their 20s while my younger brother was born when they were in their mid 40s. I would have to say there is noticeable in the way I was raised versus the way he was raised.

Since my other siblings were born between 1982-1985 we were all pretty close in age so a lot of times we didn't get a lot of individual attention compared to my younger brother who was basically raised as an only child. Also, I would say my parents were a lot more disciplinarian with us than him because since my parents were a lot younger when I was a child, they had the energy to keep up with any antics I was doing and also didn't put up with any bullshit either (my grandma, who died when my younger brother was a toddler also played a very active role in my upbringing too so my parents could dump me off with her if I was being a handful) while with my brother, they were definitely a lot more laid back discipline wise and as long as he wasn't breaking something or causing bodily harm to himself or to others, my parents were just happy to have him distracted with something.

I really guess it matters on the parents and how they bring them up, and having an older parent doesn't necessarily have bad effects...for one thing, my brother is a lot closer to my parents than me and my other siblings...he also does a lot better at keeping himself personally entertained while also possessing a lot better social skills (and less shyness) than I had because when you grow up with siblings your age, you have them to hang out with and don't necessarily need to go make friends if you don't want to (or you share the same circle of friends) but if you're raised a single child, the only way you'll encounter people your age is by socializing and making friends. My younger brother is really good at that.