If you expect to get and exotic or cool car for $4000 your going to buy nothing but trouble. The only way 4K will get you something decent is to buy a plain jane car where you get the best bang for your buck. Getting something exciting will cost you more in long run.
With 4 k in your pocket take BMW off your list unless you have dad's bank account to keep it going.
Think Accent, Elantra, Yaris, Corolla, Versa not Camaro, Audi, BMW, Charger.
I was 16 once and know what you want but will cost you.