I must say that I do not know any programmers who have lasted into their 50's without being regular stoners. Something about cannabis seems to protect them from the dementia that is so prevalent among people in this field 20 or more years.
Relative to this article, though- even though I'm a big advocate of the herb I'm familiar with the research done in Israel, Spain, and elsewhere, and one common thread is that cannabis alters the growing brain in ways that may not be desirable. I wish we could talk to our kids intelligently about it. Whether it's legal or not, it is not a good idea for a teenager to smoke a lot of weed. One puff isn't going to kill you, but once a week might impact your brain, and give you less psychic space to explore when you get high later in life.
Patience, children!
I've always used a company's drug-testing policy as a litmus test. If they test for cannabis, I know that they are limiting their pool severely, and that they will not get a number of the best programmers.
I wish there was a good study on mental health in aging programmers, to validate what has always been obvious from experience. We have a shelf life. This work is challenging and affects your brain chemistry if you spend your career constantly immersed in difficult programming tasks.
The guys who smoke don't seem any less sharp than the other folks I know in those age groups, and they seem on par with the other folks I know of all age groups when they are smoking. So yah, I know plenty of wise old guys who regularly smoke.
That's an honest question, my own connections do not include programmers over 50 that smoke marijuana regularly so I'm curious how many people would bill themselves as such.