Thanks for trying to straighten us out. It turns out, none of us were right!
When the world of Celestia was first released, the minimum was indeed 48, but KingsIsle has lowered it since then. That's because they also streamlined a lot of lower world quests so people can get to higher content ASAP.
According to the game updates page for January 2014, the minimum level for Celestia is now 44. The change was made on 12 February 2014.