I tried to join the military when I was 22, and was turned down. I was, and am, willing to fight and die when it's necessary to stop evil.
As I said, and you clearly ignored, I would be a liability to Ukraine where I am right now. I am old and slow, and that would put younger, fitter people at greater risk of being killed than if I wasn't there. What I can do is vote for politicians that will fund their military, donate money to specific units for things like buying drones or Hilux trucks to move fighters, and so on.
I'm aware that Ukraine has a corruption problem. That's not actually material to Russia invading and killing civilians. Louisiana has a corruption problem; that doesn't mean that Mexico should invade and bomb New Orleans' French Quarter.
We're not talking about Vietnam, Yemen, Afghanistan, Iraq, or even Korea. I opposed our invasions of Iraq and Afghanistan, because I predicted--and quite rightly--that our invasion would cost tens of thousands of civilian lives. In Syria, we should have followed through with our commitment to the rebels when Assad used chemical weapons, and we didn't; the result has been that Assad has been free to wage war against his own people, and hundreds of thousands of Syrians have died or been displaced. But none of those are Ukraine. In Ukraine, Russia is the one killing civilians, and attacking civilians targets; Russia is the one that invaded, without provocation. There was no military attack against Russia or the people of Russia by Ukraine; Russia had stolen Ukrainian territory in 2014, but that does not make the Crimean region Russian.