The genres I write for are horror, thriller, supernatural, and Noir. I used to focus on Gore horror, but I've slowly transitioned to psychological horror. For me, it helps to deal with stronger characters development and interactions.
That being said, the comics I've been planning deal with adult themes, some being darker than others. Of course, I don't tell those themes explicitly -- I prefer to give subtle hints and show when it's necessary. I would say that my target audience are generally adults.
Even though I did read some mature works as a kid/teen, I'm still wary about having minors read my works. It's not that I don't think them mature enough to read them; rather, I think sometimes it doesn't hurt to wait a bit longer until you're older to read those kinds of things. Of course, on the internet, I have no way of knowing unless they explicitly tell me.
In any case, I would always try to leave a warning of some kind for my target audience. Even some adults wouldn't want to read what I write (not to say it's real NSFW -- just some of the themes). I just want to respect that by providing warnings so that people have that option to back out should they need to.