The only way for you to know for sure is that if he agrees to go somewhere private with you even if you're another guy.
With their boyish looks, their slender bodies, and their innocent smile, it's hard to think that there is a chance that these boys who are in their late teens are actually gay. Even their way of talking won't necessarily give out their sexual orientation, because they're good at keeping it a secret to the world. Most guys in this age bracket are youthfully attractive, have little to no facial and body hair, and have a slim or average body build. In this day and age, it's hard to guess if a handsome young guy in his late teens or early twenties is straight or gay.
