[CaptWillard]

I've known a lot of academics and more than a few (adult) athletes, and in my experience, cannabis is quite popular in both crowds.

[dieselgate]

I think above commentators may be referring to heavy multi-times-per-day usage patterns rather than casual or semi-casual.

[dyauspitr]

Generally when they get much older in my experience and pretty infrequently. Most problematic cases start before they are 25.