Can't Queue for Rated Battlegrounds/Arenas

You must be at max level for the current expansion

Retail WoW :
- You can queue for Rated Battlegrounds in part of a premade group.
- You can solo queue for Rated Battlegrounds since 10.2 ( WoWhead )
- You need to reach a minimum PvP item level to join the queue for Solo-Rated Battlegrounds.

Cataclysm Classic : 
You will queue as a group for exactly 10 players. More information can be found on WoWhead  

If you were disqualified from rewards for the current PvP season, you will be unable to join Rated PvP matches until the start of the next season.