Mentally, I suspect I reached full maturity in my mid twenties, and so didn't need to self-improve much after that. I never made a transition from child to adult as such, which NT's seem to do, but then, I never had any interest in following "role models" of any kind, preffering to make my own decisions, according to my own observations and analysis.
What's the big deal about "growing up" anyway? It always amused me when other pupils wanted to be refered to as "students" when moving to the sixth form, as I couldn't see the point! Right now, I've just turned fifty, going on twenty five, and that suits me just fine.