I think this kind of sexual evolution as we age is a lot more common (maybe normal, for people that fully explore their sexuality and allow themselves the harmless, daily joy of cumming, haha) than you may think.
I'm in my early 30s now, but when I was just barely getting on the Internet at 17-18, the only thing that would turn me on were super fit, tanned bronze, flawless, gorgeous model-types. I would seek out porn and I'd basically be stuck with Bel Ami (incredibly hot to the younger version of myself), or Vivid entertainment or something. Oh, and um … I've been jerking off to both gay and straight porn for as long as I've been watching porn, so don't feel weird about it.
What kind of imagery can get my motor running has changed since then, though. I totally get it. I never used to like scrawny little feminine twinks, but Staxus and Helix make some of my favorite scenes now. Probably my favorite type. Also, I used to be really really confused by "tranny" porn, allegedly made for straight guys, but I've since watched a few things along those lines and been really turned on. I always understood wanting to fuck a pussy, or a guy's ass, but for some reason a woman with both tits and a dick just seemed like "someone else's thing" for me, and then all of a sudden ... it was different.
I dig the BBC (big black cock) interracial things too, a monster of a black cock penetrating a petite white partner (male or female). The imagery is intense, of course it's hot! There's a few scenes from Staxus that are gay but inspired by interracial white porn you should check out, if you're finding yourself like this. Also, look up the performer "Goldie" for the straight videos.