Don't worry about the age, it's completely fine (in my opinion).

Regarding the sex, you have several choices. One of which is to just chill out and if he tries to pull out his shit when you're not ready you can say "bitch no." However, you can also tell him up front. The thing is, the second one seems very "in your face" and I wouldn't like that at all; and yet the first one would seem like you're rejecting him.

Things lead to another. Making out > feeling that ass > feeling those titties > down the pants etc etc etc...

If you decide which point you'd like to stop it at, you can prevent it from going any further with your body language instead of verbally (unless, of course, he confronts you).

Best of luck.