I believe that those were simply your son's wishes, but a family court judge would need to approve it. The boy's mother will likely need to be served notice as well.

I would be tempted to wait before filing for SS benefits until this has been resolved. It's not uncommon for deadbeats to push for custody rights when there's a monetary incentive. You could still find out if your son even has enough credits at your scheduled appointment. I'm not sure once SS is alerted that you can delay things or not?

Hopefully Janke will pop back in and can advise you.