When I was there earlier this month, the cover charge was $7, and it's worth every penny, in my opinion. The piano players are fantastic--my favorites are Scotty and Ray.
Jellyrolls is open every night--365 days a year. Doors open at 7:00, and the pianos start at 8:00. There is no need to get there at 7:00, though--it usually doesn't pick up in there until 9:30 or 10:00. Tuesdays are the busiest night in there--cast members get in for free.
Your son's driver's license will be fine to get him into the bar.
Karen