How much sex is enough sex?

My boyfriend (38) and I(25) have been together for 2 1/2 yrs. we decided to move in together a little over a year ago, and that's when it all started. We do not sex as often as we did when we were living separate. He tells me that he is not a sexual person and he uses his age as one of the factors. I don't know what to do. I think that sex is a very important part of a relationship. Please help~