I do think this is very different than other discussions such as wanting your kids to go to the older clubs years before they are allowed. In our case, all the DCL blogs and previous navigators that we had seen said 10+ so our son trained for it. We found out shortly before our cruise that at some point recently, they bumped the age up to 12. We couldn't find any official policy change and it doesn't sound like there was a grace period for this transition. Given the circumstances, I don't feel ours was a case of not wanting to play by the rules. It was a case of DCL changing the rules on us with no notice or warning, which excluded our son from participating even though he was still only a few months shy of their new age requirement.
So you cruised recently and the age to register was 12? We were on the ship 2 weeks ago and the age was 10. This was on the Magic and both times on the B2B we really didn't have a lot of runners. Were you on the Fantasy or Dream, maybe for some unknown reason the age difference is there?