I touched on this a bit with yesterday’s subgenre, Paranormal, but actually, in reality, there is quite a bit too young adult romances. Now when we are writing young adult romances you are going to go for writing to older teens like somewhere between the 15-18 range, which means that your characters should be somewhere between 16-19 maybe even 20 but don’t push the bracket on placing them to be older than that. Basically, when looking at writing for teens/young adults the rules still apply and one of the biggest ones for teens is that the like to read about some teens that are bit older than what they are currently.
That also being said you can also focus the niche for your book to be a certain reader, such as the one that is either still waiting for their first love or they are going through their first love but have yet to experience certain things with that person. Now the biggest question around these type of stories is the subject of sex like you would find in a regular romance novel, and the answer is you can have some but not the extent that a normal romance novel would have or even an erotic romance novel would have. This is where rating your book becomes important, and then if your book was a motion picture you can rate at PG-13 and that is about it.
Granted, the main subgenre of romance that teens are faced with are usually paranormal romance, there is the occasional historical period piece, and then there is the contemporary novel other than there is typically where romance in young adult novels can be found.
Also when it comes to writing young adult romances, you can also write for middle-grade but as far as romance goes, it’s going to be awkward, puppy-dog love, and there may be kissing but no sex. I would really suggest when it comes to writing romance for young adults/teens that you really do your research as far as what is accepted and what is not for the age that you want to write your book towards.