I agree he's not a normal 38 year old but he's autistic, most autistic people lack the social skills and the life experiences people their age have, most autistic people also suffer from mental health issues (According to
this 80% of autistic adults currently have or in the past suffered from a mental health condition).
It's just I don't like the idea of "Younger on the inside", it's he's immature for his age, maybe I'm being pedantic but saying someone is mentally younger sounds like the start of a slippery slope to trans-age where they say things like 'Oh I'm not a pedo, I just happen to be mentally 13 too!'.
Also he might not have learned why he looked so dumb with his attraction sign but Chris did learn not to do it again, that kind of thing was probally what he missed out on by not hanging round with peers in high school who would tell him things straight instead of everyone just treating Chris like the special kid.