Bf smokes weed

So my bf has been smoking since he was at least 7 years old... I know that's hard to believe but it was just introduced to him in at an early age. I'm 18 and he's now asking me about it to see if I'm interested in doing it, but I don't know what to tell him I've grown up thinking that that's bad. But I just don't know how to respond, he won't be angry I'd I say no so idk tho.