One would think that at the Age of 21, you would be concidered an Adult and be left to your own devices.
But no, its not Age Discrimination, its called "Your father protecting is little girl", a force of nature that should not be reckoned with, for fear of his wrath.
You need to sit down with your Dad and talk with him about this, get to see things from his perspective. Just because he won't let you do something doesn't mean he doesn't have your best interests at heart.
If you live in your Dad's apartment, I hate to break it to you, he does get to dictate the rules for living in said apartment. If he says "no, you can't date that guy" and you want to continue living there... well, you do the math.