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.

[fastforward]

Some people never grow up. Hopefully your brother does get probation if he's going around stealing other peoples property.

[Matt]

Yeah some peeps with ADHD can't grow up.