How to elope a 13 yr old girl and start a new life in another place?

I have a gf about 20 yrs younger than i. she is aggresive though, and asks me to take her. Our relationship is of course, illicit and only us know. i want to live a new life with her, but i need to know probable steps in living in a new place with a 'kid'. How can i p off the legal aspect of it?