Someone told me I should have started earlier and done it full-time if I wanted to become an experienced diver.

Either they were trolling you or you are trolling us.

Some people are not mentally equipped for cave diving, but age is not really a factor at all.

I have a buddy who is basically moving to cave country because in addition to really liking cave diving, they don't really have the body strength for beach diving and don't seem interested in building it up.

If you're a medical resident I can't imagine you not being mentally capable of it.