No nudity is allowed. All posts there must be marked NSFW. It complies with the ToS...
Imgflip, just like the rest of the internet, has some 'racy' but fully legal content. Minors (and anyone offended by such imagery) should just keep the NSFW boxes unchecked, for their own safety and peace-of-mind.
When I was your age, there was no internet.
But there were catalogs, and Biker and Lowrider magazines - that were right on the racks at the local supermarket. There was National Geographic, Sports Illustrated Swimsuit issue(s)etc.. And then there were magazines like Playboy and Penthouse etc. - that on occasion we might come across, whether by happenstance, when they were discarded, or because we knew where they were hidden. The bottom line, is that self-control is a big part of the Choose-Your-Own-Adventure story, called life. It's up to you and your own conscience and faith or what-have-you that determines what you're going to see.