In a society that encourages us to ingest a variety of chemicals for every perceived personal need, from pain relief to mood stability to fighting germs, as well as featuring a mood-altering substance, alcohol, as a central factor in adult social life and even business networking, I think it is at best ludicrous and at worst hypocritical to suggest that use of marijuana is in itself indicative of immaturity. There may be immature people who use marijuana for immature reasons, and do so intemperately, but this does not mean anyone who consumes pot without a "medical reason" is one of them.

I can't smoke it regularly myself because it creates more problems for me than it solves (makes me more hypersexual, amoral and paranoid than I already am) but that's not the case for everyone. Some find it relaxing the same way I find two small glasses of wine in the afternoon relaxing. Some find it eases their anxieties. Some are mature people who are simply making use of a substance that has been (stupidly and ignorantly in my opinion) unnecessarily vilified and criminalized in our modern society, which doesn't help the agenda of keeping people away from it but rather simply encourages MORE irresponsibility with it than if it were decriminalized and age-restricted like alcohol and enjoyed the same objective education about its potential dangers and bad side effects that alcohol does.

I think if you love this person you need to decide objectively whether his pot smoking IS a problem for HIM (it can be, but doesn't have to be) rather than assume it is just because of social conventions. Obviously it's a problem for you if you're uncomfortable around it regardless, but determining whether he's just a casual smoker who can handle himself and his life OR whether he is using it as a crutch and/or his use is "abuse" that interferes with his life will determine how you need to approach the situation. Asking him not to do it with you or around you is one way to approach it. It would not be appropriate to approach it like "he has a problem" unless he really DOES have one -- and again, you need to assess that objectively first, and by "objectively" I mean NOT according to the kind of hypocritical ignorance in our society that will push a pharmaceutical solution for everything and then claim lighting up a joint after work to relax constitutes "a drug problem" ... but with wisdom free from bias. Is it interfering with his work? His ambitions in life? His ability to take pleasure and have enjoyment in non-pot-smoking pursuits like sports or hobbies or whatever else he is "into"? Those would be "red flags". But if he's functional and can enjoy activities without NEEDING to be high for them, there's no need to worry except to establish your comfort zones in your relationship with him and have that respected.