Sex drive isn't good...

I'm 20 years old and my boyfriend is 35. I'm going to get straight to the point ... My boyfriends sex drive is not that great. Most of the time I initiate sex because I'm horny all the time. We live together and have a good relationship but I can't understand why sex is an issue. At least to me... I'm young, should he want me more?!! I don't understand. I mean, he's always tired and I get it but I'm starting to feel insecure about myself. One time he told me he didn't see me as an object. That never left my mind. I don't know if it's because his tired all the time or whats really going on? I hardly ever give him head, I used before all the time, Even when he was driving but since he doenst seem to be into sex so much I stopped doing all those things. He brings it up sometimes but I tell him he doesn't try and it's always me plus he hardly ever eats me out. I know he isn't cheating because he shows me a lot of affection and love. Treats me right and respects me but WHY IS SEX AN ISSUE? 
I have one last question. Although I'm very horny, I understand it's because im young as apposed to him being older. Shouldn't a man his age be horny and want to have sex with his girl simply because she's younger? Isn't that an attraction? Even if I was 25,would he still be the same?