<p>Cambridge has entire colleges that solely house students over 21, so it wouldn’t be odd at all for you to be entering as a 20 year old. A lot of British students start college at 19.
Cambridge prefers that Americans contact them between May and when they begin applying (Overseas applications are due in mid October if you want an interview). So when you call or email or whatever, they can tell you what they want from you. A lot of British schools will consider AP courses as A Levels, but they may also take your college grades, as A Levels are to some extent more similar to college courses than to High School ones. They’ll probably want SAT scores, SAT IIs, professor recommendations, transcript. You can check out the UCAS which is basically the British comm app, to see what most schools request.</p>
<p>I’ll be applying to Cambridge for 2010 admission too. I hope we’re equally lucky.</p>