I would say "too much" is when it interferes with your daily life. The vibe I'm getting is that he probably doesn't think it is too much, but I do agree it's a bit out of line to go doing it in other people's houses. This isn't necessarily too high a libido and he has to do it, it might just be lack of willpower and he's thinking "what the hell, no one is going to notice if I do it now."

As for the fantasy... If he was always inclined to picture women with big boobs during activities, I shouldn't think the fact that he's 44 will change that. It's a part of his Man Thing. That'll likely be something he hangs on to, age regardless. How young is young, anyway? If we are talking creepy, then I can see how you'd be concerned but unless you think he's actually a threat to young ladies I guess you could just ask him to keep that to himself. If you are talking of consent age and above then it might just be that that's where his brain left a mental age marker and even though his body has got older, that's still the place where he pictures his ladies.