This appeared in the uesp wiki. To determine the level of your follower/whoever (I used Lydia) drop into the console (tilde key). Target her face with the cursor and click to get her code. If you click on her body, you'll most likely get the code of that particular piece of armor. Then type Getlevel and the code. Chances are her level is the same as yours.

I've read in quite a few places that she doesn't level up. Apparently she does.