I agree with learning how to drive the car before you mod it. If you get a 99GT, you'll be behind the wheel of a car that can show taillights to some of the most powerful cars on the road just a few years ago.
I've seen a few too many crash stories from new drivers lately, so be careful. Treat the GT right, and it'll treat you right.
Sorry, I'm a little too old for you, 24.
Have fun.