Hi,
My 13 y.o son lives w/ his father in VA and I live in AZ. Custody was decided when we all lived in AZ and ex moved w/ him to VA. If I want to get custody or modify the agreement , do I file in AZ or in VA? Would either parent have to travel for court dates?

Where the child is lived, is what state takes it to court, and yes you would have to travel to court, unless you lived there

Did AZ grant permission for the custodian parent to move to Va with the child, if not AZ would have jurisdiction over that matter.

AZ did grant permission, my son wanted to move at the time, so I agreed. Now he wants to move back. Does his age give him any leverage towards this?

The change in custody would have to go through Va now, and yes your son wishes would have to be considered, but not necessary granted. Speak to your ex about this if he is willing to do so.

If the original custody order was issued in AZ, then that's where you'd file. Whichever parent(s) would have to travel to AZ to attend court would bear that responsibility.