As long as you're drinking 6 years underage, and smoking 3 years underage, why not pick up a joint?
In Australia the drinking age is 18 so im only just over 2 years under, and it is legal to smoke at any age here (in western australia at least, not sure about other states (they made it a law because whenever a cop would try and stop a kid from smoking they got the stuff)) but it is illegal to buy smokes under 18 or for someone to buy them directly for you, so basically the government is saying smoke all you want but only steal them!
Anyway i have done weed before and it just wasn't up to my expectations, IMO its just not worth the time or money, besides all the potheads at my school keep going on about how it doesn't affect them and you cant get addicted yet 100% of them are and are the biggest dopey failures ive ever seen (not saying everyone who does weed is, no offence)
But i guess the main reason is that weed has stuffed up my family severely in the past and i don't like to be reminded of it.
The reasons i do what i do,
Caffeine - I am addicted but yeah my body can't keep me awake on its own anymore
Alcohol - mostly just for fun and partying
Smoking - relaxing as forget and every now and then i really need to be relaxed.