Of course shoujo has its own tropes, and pretty often shojou repeat shounen route with 100 chapters of beating around the bush just for single kiss in the end. But on other hand in lot of shoujo manga we actually see people get together as couple, split, have sex, not being virgins, have exes etc. And it's not always fluff and moe, shojou genre really likes over the top drama, bullying and rape or attempted rape scenes for some reason.
Seinen romance could be anything. Honestly I don't remember lot of seinen romcoms besides Kaguya, but common romance is usually mature, on par with josei.