You have an '04 that probably isn't paid for yet. Financially, this makes no sense.
You're also 19 and this car has 93k miles on it. Do you have the time and money to invest when the car has mechanical problems?
I'd have to agree. I'm 21. I went down that road. I had a fully paid for 2002 Celica GT when I turned 18 in 2002. I looked at trading it in for a 2003-2004 Celica GTS with a manual (mine's an auto). I even looked at a used supra like you. The numbers don't add up. You'll be getting rid of a brand new car for a car that is almost 12 years old! It may have been taken care of, but it's at the age and mileage where problems will soon start to arise. Unless you are sitting with deep pockets, let it go.