What i have seen here though is several videos of WRXs with relatively minor mods running rings around porches on a track..
The best mod in the world is the guy behind the wheel. A good driver is hard to beat.
Kenny, check with some of the other clubs for the 18 age limit. SAFE Motorsports requires experience, as such they do not have instructors and require drivers to be over 21. Chin Motorsports has instructors and may have a lower age limit. Panoz also has open track days where instructors are available and may have 18 age limit. SCCA, BMW, Porsche, etc. may have something for under 21 also. I'm not sure but you should look into them anyways.
SAFE Motorsports is the best value around - 5 hours of track time in one day for $225!!! The other clubs are a bit more expensive but still reasonable, however you are limited to approx 2 hours of track time. Check them all out. You'll be addicted.