Sexual abstinence is when someone decides not be sexually active. Being abstinent is a conscious decision that one makes and you can make it at any point in your life. You can make the decision in your teens, 20's, 30's, 40's, 50's, and so on. People have all sorts of different reasons to choose to be abstinent. For whatever reason you're being abstinent for whatever personal reasons you have, you want to make sure that you come to that decision on your own. It shouldn't be your partners decision whether or not you choose to be sexually active.
One of the biggest physical benefits is it prevents pregnancy so refraining from sexual activity will not have a chance of getting pregnant so this is a pro if you are interested.
It also prevents STD's which are diseases which are infections thats spread when people take part in sexual activity.
If they ask if you want to smoke, simply say no. If they don't respect your decision or try to force you, then call a trusted friend or adult and leave