@Greendot,
What I find weird isn't any of his fetishes, but that looking into his laptop is a crime in your relationship (whenever I start dating someone I always take it as a compliment that she wants to know more about me by snooping into my personal stuff). Or maybe that's a symptom of taboos between you? Taboos aren't a healthy thing in a relationship.
I'd say this:
1- on the bright side, he's getting turned on by old ladies, but having sex with
you. Worse would be if he was getting turned on by some old lady and having sex with
her.
2- It doesn't matter if you find it gross, his tastes are his tastes. I find some old ladies attractive, though I'm not really into old lady porn. Sometimes I also find it exciting to go over my limits and masturbate to people that usually turn me off, or to even try to find turn ons on them. His fetishes aren't really something you should be concerned about, even if you can't fathom. As long as they aren't criminal.
3- What to do? Hard to tell. It's a matter of you digging into what exactly is going on there: if he's using porn to get turned on before sex frequently, then maybe there's something lacking in the sexual relationships between you both. Try to see whether he's really there with you while having sex, or if he's distant. If he's distant, that may mean he's fantasizing about something (that may involve you) or that he's thinking of someone else. Thinking of someone else is not necessarily a bad thing, unless it's an IRL lover, or unless it's a symptom of him not feeling so attracted to you anymore. It may happen that he feels your sexual relationships have become monotonous and boring, and he's trying to add something refreshing to them. That would be good news, because boredom is not a big deal and can be easily solved by using your imaginations to make sex fun again. Because sex should always be fun.
That said, there's also no substitute to talking things through. That's why taboos are harmful.