according to federal law, you have to be 21 to buy a handgun(there are ways around this)
That's not completely true. Fed law only says that a FFL can't transfer agun to anyone under 21. It says nothing about actually purchasing the gun. FTF sales are perfectly legal for anyone 18 and older as far as fed law goes. (states may differ on private sales and age though)
I agree with kingcheese as far as going for a quality gun, but for different reasons. Choosing a higher quality gun (and a bit more expensive) shows not only that you are looking for something to last and not just something for a quick thrill, but also that you are willing to sacrifice to achieve that goal. There is no need to go all out on a brand new thousand dollar HK, just something that is a bit more durable than a hi-point. Maybe one of those P6 imports that were about $350. Nothing says class like a Sig!
A better gun will also last longer. For example, my family has a gun that has been handed down for over 100 years and is still in good working order. Wouldn't you want your first pistol to be something your great grandkids can shoot?
Also, and this may be some really bad advice depending on your specific situation, but assuming you're out of the house already, your parents don't have to know about any guns… (which would mean private transfer only)
And for the record, some parents just can't be convinced. My parents funded a 14,000 round/year competitive shotgun habit, but flatly refused to get me anything approaching a rifle or pistol, including a bolt rifle strictly for range use. They still don't know about any of my pistols…
+1 on getting into some form of competitive shooting. But be warned, it's very addicting. I started out with the intention of just doubt a little here and there for the fun of it, and wound up loving it and traveling across the country for competitions every week!