Especially when I'm looking at the newer 2nd Dans, I'd say there is a big difference in skill and knowledge. It took me 5 years of training to get from Nidan to Sandan. Age has it's effect. Kicking, for example, is a skill that deteriorates with age and accumulated joint injury including age related joint injury. On the other hand, tuite, making things just flow and work logically, managing a class and being able to teach,explaining bunkai, being able to improve your art with knowledge from training outside the school curriculum, knowing how to integrate what you know into a cohesive whole... these things have all improved for me over the past 4 years.
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The older I get, the better I was!