I'm 41, he's 44. Married 10 years, kids 9 and 7.
My sex drive just isn't very high. When we first got together we were at it like bunnies, like I imagine most couples are at the start of a relationship. Kids came along, it dwindled a lot but has since improved now they're older. However, DH is horny all the time, he thinks about sex all the time, but I just don't. I'd say it's usually once to twice a week and when we do have sex it's great, I always think how we should do it more, but life happens and I'm always tired or just don't think about it.
He rarely initiates it, because if I say no it gives his self-confidence a whack. Yet he doesn't want me to say yes and do it just to please him. He wants me to do it because I really want to. So it's up to me to initiate it and I often don't because it doesn't cross my mind / or it does because I know he wants to but I'm not in the mood.
I do sometimes get really horny and I'll jump on him at the first opportunity. But he really focuses on the times he tries to start it and I say no (despite there being lots of times I do agree!) and it always eventually starts a conversation about what "the rules" are when it comes to sex. Why is it always on my terms. We go round in circles, because he doesn't want me to have sex just for his sake, yet I don't always want to so I want to be able to say no without feeling bad, yet if I want to have sex then he says yes because he's always up for it...so that makes it always on my terms! I see his point, but I just can't get it through to him that I just don't think about sex constantly, the desire isn't permanently there like it seems to be for him.
Everything else in our marriage is great. Just to add - it's not that I don't find him attractive, I do, I'm certainly not hunkering after other men. I know he adores me and fancies me, that's not an issue. I just can't magic up the desire that he wants me to have.