It really takes a lot to pick up on drugs after you have gone without them in High School, if you've gone through High School without touching drugs, I'm pretty sure one is set for life, but you have another story my friend.
So why did you start if you turned it down in HS?
I've had rheumatoid arthritis since I was 14. So my joints are swollen all day, every day, without fail. I haven't gone a day without swollen joints and considerable pain in almost a decade. So being sick of being in pain and since I refuse to take harder drugs doctors have suggested (oxys,stuff like that) due to me having a very addictive personality, I see no way I don't become completely addicted to them and I'd be the type of guy that never gets to rehab, he just dies. If 1 is good 30 is better to me, so I steer clear of that and drinking, although I drink occasionally (I rarely drink, I hate the feeling of being drunk).
So I decided to start smoking after trying every other alternate to harder drugs and nothing worked. Weed works 100X better than anything I have ever took before. I used to be one of those people who hated weed and thought it made you lazy because all my friends did was fuck around on it. I then tried it myself and I'm far more ambitious on weed and I get far more done in my life while on it than without it. I learned about all the misconceptions about weed through documentaries, reading books and listening to Joe Rogan (may sound odd, but the man is a fucking weed god and one of the most intelligent men I have ever heard speak, ever).
It basically helps me with everything. I can better access the frequencies I need in life to accomplish what I need to, the way I need to. I'm not high all the time though, although it may sound like I am. While that would be fan-fucking-tastic and there have been stretches were I basically lived the documentary Super High Me (smoke weed all day, everyday) for a few months, I go stretches without it and I'm fine. Things are far less fun, but it's not something I physically crave or realistically need. When my fiance was between jobs I got far less weed than usual due to finances and was able to make it. But then again there is someone like my fiance's brother who needs like 10 grams a day just to function and pawns shit off for weed all the time.