So I understand that whether due to construction, or simply a bug, followers do not level with you. I've heard that their level is locked in when they first "spawn". Does this mean (using the example of Aela the Huntress)

1) The first time you enter the same cell as the follower (IE the first time I enter Whiterun)
2) The first time you are able to use the character as a follower (when you complete "Glory of the Dead") or
3) The first time you enter the command mode with a follower (the first time I say to Aela "I need you to do something")

Thanks.

To my understanding its when you unlock them, so when you have the option of "follow me" is when they are capped.