Where in the bible does it say wait till marriage...?

Im a devout christian, but Ive debating with things lately. Like the whole waiting for until marriage. I notice that people I know who follow that rule end up getting married really early like early 20's and with school, I dont want to get married till im done or almost done getting my bachelor's and md or phd. That may take a while, and I dont know if I wanna be a 30 year old virgin. I read the Bible every day, and I never see anywhere that says, "wait till marriage." I see things like how ual immorality is bad, eg. adultery, sleeping with someone who's married...things like that. But where does it say no until marriage. Like I can imagine being sooo in love with someone, that you could see yourself marrying, and sharing that with them, but not marrying because you want to wait for a better time. I just dont wanna be listening to false things when it comes to abstinence until marriage, because when I hear that its nowhere in the bible, but just the pastor says it. So if im listening to him instead of the bible, wouldnt that be a form a false gods if what he were saying wasn't from the Bible. I just need to know its in the Bible before I follow it, you know..? gosh this is so long.