it really depends on the person. I have a friend who has done it for years. He is an accountant, makes nearly six figures and is a wiz when it comes to numbers. My buddy who is a mechanic has done it all his life.
my neighbours have apparently smoked it pretty much all their lives. Judging by the fact that they sit around their yard smoking it with their children, so have their children. Both of whom are high-school dropouts, by the way.