I don’t see how it would be much different than enjoying a few drinks with him?
I personally don’t smoke cannabis for no other reason than I don't enjoy it. Tried it a few time as a teenager and had a space cake in Amsterdam a few years ago, don’t see the point in it, it just sends me to sleep. I’d rather have a gin and tonic any day.
However I have no problem with cannabis, obviously if somebody’s dependent on it and feels the need to smoke it every day it’s a huge problem, in the same way it would be if somebody was an alcoholic and felt the need to drink every day.
It’s all about moderation.
I think if your son has a mate who has some and he’s around it, once the lockdown is over and he’s out and about with his mates it’s likely he will ‘experiment’ with cannabis anyway. Also, he’s 20 years old, he’s an adult there wouldn’t be much you could do to stop him even if you wanted to.
I wouldn’t recommend it, just because in my view it isn’t much fun. But if you want to, and you think you would enjoy it, then why not? I personally wouldn’t encourage it. But keep an open dialogue with your son about it, that way he’s less likely to keep secrets about it from you in the future.
If you’re going to do it, make sure you read up on the effects and how much to use etc, and start off with a very small amount as others have suggested.
Look after yourselves x