That could be, in that case isn't Russia's violent aggression against its neighbor that much more tragic? And isn't that even more rationale for non-Ukrainians to support Ukraine more and oppose Putin and Russia more?

It could also mean that the whole country is behind the war effort and EVERYONE is fighting because they know basic history and understand the horrors that follow Russian domination or even simply that foreign invaders are in their home and they aren't standing for it whatever their age.

What was the average age of someone involved in the fight against the American occupation of Iraq? Likely not 18. Likely not 22. Probably more like 40. And are the Americans still calling the shots in Bagdad? Nope they are gone because the 80+% of the citizens wanted them gone. The relative populations of Iraq and US are similar to Ukraine and Russia. If you don't have to fight just the men of fighting age but the whole population from kids to elderly and both sexes the war gets a lot harder. Maybe it is a sign we should encourage the Russians to stop invading instead of telling the Ukrainians to surrender to the bully.