30+ to get into Abyssea, but exp scales down. I'm not sure how much for lower levels, but I know 79 gets -5 per kill compared to 80, another -5 for 78, etc. I'm not sure if it's linear or not...
Either way I want to try it with my WHM60... it might be slow to start but even if I'm getting 1/4th of the exp it's still in the exp party range (give or take, assuming we stay long enough).
It's kinda crazy to me that it's easier to get a full alliance out in abyssea than it was to get a full party and find an open camp (not that doing that is hard, but getting an abyssea alliance seems easier atm).