Do some teens not grow up until they are well into their 20's?

[Mommy Is In Menopause]

My brother is aged 20 and has some LD/ADHD issues. He at age 20 does foolish things and has an angry temper like he is 12. The temper is monthly blow ups down from daily when he was 15 and weekly when he was 17. He still does stupid things and is going to court for shoplifting. I kind of hope he gets probation so he learns a lesson. He is also said by my parents to be sexually active (they find condoms in his room and a sexual message on his Facebook page a family member saw).

Is this likely who he will be the rest of his life or is this common at this age and he will grow up by 25? Does LD/ADHD make one more likely to these behaviors? I was Learning Disabled but only acted maybe 2 years younger then my age and any misbehavior was minor. He is sophisticated however whereas I was not very social and known as the "golden one" in terms of spending time with parents and being respectful. My other siblings don't have LD and all grew up normal.

[Kenneth]

I'm 30 and still not fully grown up. Can't get a job due to the horrible american economy even though I have 8 years of working experience.

[Corina]

Having sex is normal... and the fact the he is using condoms shows hes being a bit responsible.
Everyone is there own person, he will mature at his own time.

[221]

Yes that's how my brother is. He's almost 20 and he makes the stupidest decisions ever. In fact, last night he decided to drink and drive (not wearing a seat belt) he crashed into a PARKED car and smashed his head right into the windshield. Well, his car is destroyed now, and he is in the hospital right now with a broken bone in his neck and a fucked up eye. This isn't the first time this has happened though, he drinks all the time. He's an alcoholic. My mother and I have been praying that he'd get his license taken away and he finally did last night. He has 2 DUI's by the way.. We've had to go to the hospital about 5 different occasions now because of his drinking problems.. When will he learn that he is going to end up killing himself or other people if this doesn't stop!? He is so fucking immature! He dropped out of high school in 10th grade, never finished. He's never had a job. All he does is party and do drugs! It's pathetic!

[Sarah]

Yes, I know two people (one's 20, the other is a few months away from being 20) who still behave like 13 year olds.