I'm a 21 y.o. guy...?

Just go talk girl-stuff to a girl that you would like to date and then ASK HER OUT. That would be the place to start. Being able to talk to girls and having them like you as a friend is a big plus. You cannot possible know that she won't go out with you unless you ask her to. She might say no, SO WHAT? If the first one you ask says no, then find another one that interests you and get to know her, then ask her out. Eventually, things will click and you'll start an actual relationship. Women/girls tend to be attracked to guys when they like their personalities and feel secure with them, it really isn't all about the looks, which you are probably under-rating anyway. Give yourself a chance and ask out someone with whom you want a relationship, it really isn't worth waiting until she grabs you by the hair and drags you off to the cave, you just cannot count on that happening.