There were just 2 half hour sessions on our 7 day for those under age 18, but ONLY if you went with the kids club, and BOTH were at 8:30pm, and we had late seating dining.
DS plays high school baseball and was very disappointed he could not keep up his workout routine on the ship.
I can't believe they don't have regular hours everyday for those under 18 on a family cruise ship. Heck, even the adults only clubs are open to those under 18 until 9 pm.