You should give them a order to gain experience. One of the things that I do when I questing these days is if I get a new companion and I don't want to use them yet, I make them get free training tomes for me. Companions will only be able to give you free training tomes if they are your level or above it.
hi i'm lvl 23 my the ones i'm not using are like 12!!!! agggggh my others are fine what should i do?
Since you're not using them for combat ( or tasking? ) then I suggest that you place them on Brawlin' task to gain their own experience. You can do this before you log-off. You can also give them a few tomes of their own which will boost them at least 3 levels from a single tome, since they are so much under your level.