You have only started to notice it the past year...it has been deeply popular for ages...like thousands of years. It's actually an old art form, which in modern times has taken to comic books (I used to read those secretly as a pre-teen) and film.

It's all about sex showcased in non-traditional social norms...the kinkier, weirder, more out of proportion the body parts, more visceral...the better.
It takes all kinds to appreciate Hentai. has nothing to do with age.

I've been watching and reading hentai since college. And yes, there are different types of hentai for everyone. It's good to find out what the Japanese word is for your particular kink. That way when searching for hentai that you like, you can use those words to find them easier.

A few years back there seemed to be an explosion in the popularity of Japanese culture here in the US. My understanding is that one reason why hentai is so popular in Japan is because with anemia things that are normally taboo are considered acceptable in cartoon form. Similar to the way "Family Guy" and "The Simpsons" can get away with things on network TV that regular sit-coms  can't. And the Japanese seem to be a little more open about their sexual perversions than other cultures.

so I'd understand why someone would watch it. I've gotten off to it before, but not my first choice. Just when I have a taste for something you don't see on regular people porn lol

Hentai isn't a new idea but you may see it more because of the expansion of of Internet access and free porn sites. I have gotten off of it myself and it's there if you want to see acts that real humans won't(or possibly can't) perform.