Juvenile Court: Can a Youthful Offender Get an Expungement

My son was convicted in Charleston, SC, under Youthful Offenders Act when he was 16. He is now 27. We moved to OK in 2007. His probation was served and finished in OK.
Charge was Strong Arm Robbery. Five boys left school, went down street and robbed a small convenience store. They then went back to school. My son was the lookout. One boy inside pointed unloaded gun at store owner. Take was about $200 and a carton of cigarettes. My son pled guilty under YOA. Our understanding was that once his probation was completed and he was at least 24, this could be expunged. When we tried to get it expunged, we were told law had changed and he had to be older.

This charge is coming up on background checks for job applications causing my son to be denied jobs as a convicted felon.

What would we need to do to get this expunged? Since he is having trouble with employment and I'm on disability and widow's pension, cost is definitely an issue.