Ages are permanent and can only be removed by deleting them off the hard drive manually, which is why it can be such a problem to have everyone on the server creating lots of them.
The benefit of making an age is that it is only accessible if you have a book that links to it, and those books have to be created by the player that owns the age. It's basically a way to escape griefing in the overworld to a world people can't follow you into.
So uh, didn't Steeveeo say we were moving to FTB on the 7th? :P