I think the average age of Reddit is 16. High school students have infiltrated it ages ago. This is why I don't take anything I read in the comment section too seriously.
As you can see, Reddit is overwhelmingly 25-44. The most represented group is actually 35-44. The high school demographic is negligible, and equal to the 65+ demographic.
Also, if you were to be completely honest with yourself, I bet you would not have made the comment you've made if the jokes and the upvotes were about race and lynchings instead of underage girls and rape.
That said, I'm glad Reddit exists, for the same reason I'm glad that skate parks and X-Boxes exist.