TrixieLZ, I hate to be the bearer of bad news but, if you have joint custody, no matter how much he is involved in their lives, you must get permission from the court to move your children when it is to a different state or more than 150 miles in the state the divorce was finalized in.
As for their age, each state is different but, several states has the age at 12 years old and others at 16. This can all be changed if the judge sees the children and decides that they are mature enough to make good decisions. Just call the Clerk of the Court and schedule a meeting with a Divorce Mediator. Hope this helps!!!