Me too, but I’d guess that it’s because Ukraine is a somewhat younger country, since the US stopped using the draft in '73, about two decades before the current Ukrainian government was established, so they are operating on very different standards. Just a guess, though.

WW2 left the Soviet Union without a generation of men which led to all kinds of problems after the war. It’s a lesson hard learnt. Your men need to breed before they go to war and die. Ukraine knows this and hence they keep the draft age higher.