Since nobody went on dates or spent much time alone with the opposite sex, the issue didn't come up. I doubt the question would have even made sense to people in those times. It only gets you worked up with physical longings you can't fulfill without having sex. So if you're committed to saving sex for marriage, messing around can only lead to frustration. It involves your spirit as well as your body.
Sex is meant to be enjoyed as part of marriage.
And when a couple saves all their intimate expressions of love and commitment for marriage, they experience the thrill of sex with God's full blessing. Your friend's teacher is wrong about experimentation. What I usually see resulting from experimenting with messing around is guilt, broken-down relationships, and couples who keep pushing the limit until they go all the way. There's another good reason to stay away from messing around, and that's your reputation. My advice is that couples limit their physical activity to brief kissing and hand-holding, and spend their extra time talking together, having fun, and serving others.