Well, I'm not an expert, but I don't beat less hard than when I was 22. I'm 42 now.
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The biggest difference for me is considerably longer recovery period that doesn't allows train something like I was 17-22.
Plus agility is considerably lesser ( changing angles etc. ).
& I think a bit more prone to get damaged head too, if compare with my 22 y.o version.
For this yeah, agility does matters a lot, some not bad KB coaches consider for example KB guy's prime like some 22-27 , this yeah, from euro and non Dutch approach.
& high kicks, yeah, I can't do what I was able to do when I was 22, for example.
Actually when I recently did last sparrings, I don't use high kicks anymore, It costs me too much.
yeah, longer than 4 rounds in row I spar only boxe or some grappling " stuff " ...
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I for example even compared 35+ y.o pro boxer vs 18 y.o ammy guy.
For 3 rounds 18. y.o guy was better. At least from judges verdicts in trial bout. ( now pros are eliglible to compete in trials for Olympic ranking to get in the Games ).
Longer, I don't know, this older guy fights 8 - 10 rounders, gas tank does have pretty decent but he Isn't such sharp and agile like he was some 25 y.o amateur.
Bang if landed, I think pretty not less effective tha his younger version.
And this isn't HW division, so he should make weight limits.