Today I was on my level 20 ranger, and a bunch of guildies and I decided to do some flagging for FoT. We had 2 level 20s (one premium, one VIP), and the rest of the group were level 21 (mix of VIP and premium). We went to Cabal, the leader went in on hard, and I (the level 20 premium) couldn't get in. The VIP level 20 could. We did a bunch of experimenting... I could go in on Epic Normal, but not Epic Hard. Yes, I had the quest and quest arc. I was 25k XP from level 21, so we ran a EHSnitch, I leveled, and then I could get into EH Cabal fine.
Now, I know that they've made restrictions that heroics can't be in a party with epics who are questing, and I know why they did this. I don't like it, but I understand. Is there some reason that a level 20 in a party of 21s can't enter an epic quest? There is no reason I can think of why an Epic level character can't run Epic level content with other Epic level characters.