Let me just start out by saying I don't have either content warnings or age guidelines on any of my books. In this day and age, there are probably reasons why I should, but it's one of those things I won't do.
The covers and the blurbs should pretty much tell you whether you're old enough to read the book, and that your children probably aren't. Well, maybe except for the Once Upon a Djinn series, where the most R-rated thing is the swearing. And it's not rife with curse words. I gently sprinkle them in where they're necessary. If you've reached an age where my books look interesting to you and you haven't encountered swearing before, you probably should put my books down and go back to your bubble.
As for content warnings, I'm against them. Meaty books should shock or surprise or perhaps offend you a little, and if you're reading along and come across something that you just can't handle, close the book and move on. I did that the other day. It was over the top - for me.
Maybe I should put a special snowflake warning on mine. 'If you are a special snowflake, you're probably not going to like this book.' Wouldn't want anyone to melt, doncha know. Perhaps such a warning would've prevented a one-star review/rating here or there. :shrug: They are what they are.
Of all my books, Fertile Ground is the one I worry about the most. The villain is a serial rapist and murderer. But I think I treat the subject well - I don't actually describe the acts in depth, just the before and the after - and the heinous asshole does get a most satisfying sort of justice in the end.
Of course, there is a lot of murder in my books. If you're sensitive to that sort of thing, you probably shouldn't be shopping in the mystery/suspense/thriller/urban fantasy sections.
Sometimes I wonder if authors put content warnings on their books as less of a 'warning' measure and more to titillate. Like saying 'don't read this' will encourage people to read it, just to see what the fuss is about. :shrug: I can't do that. It's not me.
What do you think? Do you put content warnings and age guidelines on your books? Do you care whether a book you want to read has content warnings?