The age policy change took place several years ago. I don't remember the exact date and I would have to dig deep to find it but off the top of my head I think it was around 4-5 years. And the reason, if you lurk and read most of the posts, should be quite obvious
Initially when getDare was launched it was just a small forum devoted to Truth or Dare with teenage members and the old posts were quite tame in comparison to today. And the whole S/M area didn't exist at that point. But over time, members got older, the site grew bigger and attracted people with different interests, including BDSM. That's where we had to make the change.