What do you mean when you say "selling" the 529? Do you mean taking all the money out of the 529 account as a non-qualified distribution? What kind of 529 plan is it?
There is no exception to the 10% additional tax on a non-qualified distribution that has anything to do with the age of the account owner (or the beneficiary).
Edited to add: if you are the account owner, you can always change the beneficiary to a qualified family member, which includes a sibling or first cousin of the beneficiary. Perhaps there is someone in this category who more conveniently goes to school in the United States?