Apparently adolescence is getting longer with people not taking on an adult life to they get past 25 sometimes. Umpteen years in college, bad economy keeps you living with parents etc..
On the other hand, Star Trek regularly portrays 8 and 9 year old children studying calculus, programming, engineering, at levels which would be good for most 2nd or 3rd year undergrad students (approx age 20) for contemporary humans. In the Star Trek universe, human mental development would seem to be about twice as rapid.
I mean, you see occasional exceptional students even right now in the real world, but they are truly the exception, not the rule, whereas in Trek, they seem to be pretty much the "normal" kids.
Ever see very early paintings of Mary and baby Jesus where baby Jesus looks like a gnarly adult? Apparently people actually had a hard time painting infants faces accurately so just made them little adults. I think Trek has the same problem, can't write kids so just make them all mini-adults and be done with it.