He has a responsibility to be a good sex partner for you. I would definitely have some discussions with him about this and that you want to encourage the sexy side of him. If things get worse, then maybe you should see a sex therapist. He might have a medical condition. Depression is the most common disease that will evaporate sexual desire.
Older partners are more experienced.
They can have more comfort with their bodies or knowledge of sexual partners and have picked up some tricks along the way. So yes, they can be better partners. It is completely normal. Everyone fantasizes every once in a while. It becomes a problem if it becomes obsessive or if it is the only way you can enjoy sex with someone.