Refer a Friend: Granting Levels from Friend

Quick question regarding this. So if I invite my friend, and they level to 60, does that mean I have a free 30 levels to gain? Or do these charges not stack? For example you gain 1 level to give, and only have 1 to give until I use it.

Secondly, lets say I have a level 29 character. IF my friend levels to 60, (and this might hinge on the 1st part of this question), does that mean i can use the auto level ups all the way to 59?

Thanks for the help guys!