Well, I've had the opportunity to observe a small sample of former adolescents, now in their sixties, who were pretty regular users of the Killer Weed at least through their twenties, and a few to the present day. These include teenagers who have grown up to be attorneys (including one judge), a couple of physicians, a research physicist, an architect, an art conservator, a lot of tech folks (including one who headed up the entire MIS operation of a retail chain with a national presence), a couple of tech writers, an urban planner, a television producer, a corporate PR flack, two accountants, two real graphic designers...all reasonably successful, and to all appearances happy and well-adjusted. Now of course, I make no extravagant claims for the breadth of my sample: there are many more pot smokers I knew back in the day with whom I've long since lost touch, and it may be that all this lot are homeless or dead, or have graduated to snorting Janitor-in-a-Drum. I observe merely that with regard to those people whose careers I have subsequently followed, I have detected no apparent harm done during their formative years.
In college I once shared a relaxing doobie with an individual (already well-known in his field) who went on to be showered with honors and awards, including a year's term as U.S. Poet Laureate. Now it's true that at the time he was no longer in the first bloom of youth, but he did reminisce about smoking weed in the 1950s, when he would have been a snotnosed (or potnosed) kid. Again, the experience appears to have constituted no impediment to success.
Just my two cents, as A.S. likes to say.
cordially,