Thera is not old enough...besides, if it were Thera we'd know a lot more about it than we do.
I think Thera is plenty old enough and given the massive destruction of the Minoan civilization that followed, I'd expect a lot of information to get lost. There is plenty about the Bronze Age that we don't know. Of course it's also entirely possible that Atlantis is simply fiction or refers to some other civilization, but I think Thera is closer than anything else that I've personally seen. Your milage may vary.