You can get into PoS at lvl 55 for xp, but for planar progrssion (to get to EP and beyond) you will need to do a PoJ trial and get flagged normally.
Edit: for your level you also have access to Torment, Valor, Crypt of Decay, Bastion of Thunder, and Halls of Honor A
Edited, Thu Nov 3 12:47:04 2005 by dfrnchman