>>713216209
Because you either weren't attractive enough to get a girl interested in you (where you would learn this), or, more likely, you were simply too dumb to realize it. I say more likely, because unless you're truly, deeply ugly, and never showered etc, it's painfully fucking easy to get a date at that age. Hormones do an ungodly amount of legwork at that age. No one knows what the fuck they're doing. High school and uni are where mid guys get a shot to know how it works. But if you don't figure it out then, your chances of figuring out later are way lower.