It can be. I don't know if this particular game meets that. There is a part where the kobold lays an egg, but as of yet I dunno if it meets the need for an 18+ rating. I suppose it would probably be best that he does, though.
Besides putting it on the itch.io page, there's the adult and erotic tags (and the top-down tag). You could also put in a screen for first time players asking if they are 18. If they aren't, close to desktop. Or, if you don't wanna do that, put an 18+ only warning in the game.
