I was on my wordpress dashboard and got intrigued by the “mature” site characteristic.

By Matt from Wordpress support:

What is Mature? If only it were easy to say.
Lots of profanity - probably.
Some profanity - probably not
A few images of topless women (for it is usually women and western society tends to see the topless man as non sexual generally) - probably not
Lots of images of topless woman - probably
Genital images - definitely unless the blog is educational (and yes, we know the difference between education and not)
Images of mutilation, dead people, injuries, cruelty, killing - definitely.
Combinations of the above - probably
Declaring your blog 18+ - definitely