He has to be the party leader (instance owner), he will get normal exp, you will get less (because you are higher in lvl than the indicated level requirement of the encounter).

Got it! 14

I'm on 12 and I didn't get acces. Why?

12/12, still not in.

Tomorrow will also be the first maintenance period, so I guess tomorrow will not get in too many people. Maintenance Window #1: Date: Early hours of Friday, December 16th (CST) Time: 2AM CST (12AM PST/3AM EST/8AM GMT/9AM CET) All game servers and SWTOR.com will be offline during this period. This maintenance is expected to take no more than four hours, but could be extended.