I would think he'd have no problems at all.
I haven't gone to the APA but it's at the Riviera right? I've seen many younger people during the BCAPL at the same place.
The Pool Area is far away from the Casino so the age doesn't matter. The only issue would be that he couldn't hang out in the Casino Area. There are walkways through the casino that I think he could take to the hotel room or restaurants.