It took me well into my 30s to walk away from religion. Especially in an isolated environment, it's likely he doesn't really understand his choices, and though he has had a much more comfortable way of life than us, it's still hard to transition to a much less forgiving way of life. I had to leave behind friends and family I still wish I had a good relationship with, but the cultlike environment (JW) is specifically designed to discourage leaving. Learning about other viewpoints are heavily discouraged, as is associating with people not in the same belief structure.
While mine was religion, with how polarizing his father is and the protection needed, I don't doubt he had even less access to other people and viewpoints than I did. I at least got to meet people online, at work,and through shows (funny enough, Futurama was a huge part of breaking me away) to get some other viewpoints, but some of my friends were homeschooled and wouldn't watch or be allowed to watch almost anything secular.
It's why so many are afraid to allow kids to go to college (pretty discouraged by JW also), because they might change. I say at 18 the chance of someone in his position being able to get alternative experiences is slim to none.
I buy THC drinks online from 3Chi. I haven't had an urge to try anything harder (in fact, I'm a bit scared of anything that might affect my heart (aside from booze becaus3 we all do at least one very stupid thing), and the only thing I do want to try but only with a good support group around is shrooms).