Private pilot attempts to exit runway too quickly and suffers an excursion.

Narrative

The pilot of the C152 was landing on Runway 30. After touching down between 200-600 FT from the beginning of the runway; the pilot started to brake and tried to exit at the next intersection; which was Alpha 7. The aircraft's speed was still too fast to make the turn; it went off the runway and came to a stop just into the grass between the runway sign (Runway 2/20); then left on Taxiway A; and cleared all runways. The reason the pilot tried to turn off on Alpha 7 was to quickly clear the runway for the jet traffic that had been cleared to position and hold behind him at Alpha 9 just after his touchdown. Afterward; the pilot realized that he should have kept the aircraft on centerline while braking to a speed that is safe for the aircraft to turn as desired. The pilot should have taken the next available taxiway after slowing to a safe taxi speed. Factors affecting the pilot's performance: 1) The pilot received his Private Pilot Certificate 6 days prior. 2) The flight was his second flight of the day; whereas he normally only flew once a day. 3) The Pilot had just done 3 safe touch-and-goes before his landing.