At age 30, no, smoking marijayjay doesn't make you cool. Much the opposite, in a lot of people's opinion. Practically everyone around my age who smokes is pretty discrete about it, and never advertises it. They have nary a pot leaf insignia on anything they own, and dress and groom themselves pretty normally, for the most part. But in the evenings when many people might enjoy a sports game on TV or walk with the dog, they smoke a bowl.
I don't really think it's possible for some over 30 to be cool, and don't know if I'd want to try even if it were possible.