first, it's factual bullshit to assert Putin invaded Ukraine to somehow "save" the separtists. Their worst case was move fifty miles and be russians, but actually Nato didn't suggest that. Putin invaded because he, and probably a maj of Russians, see Ukraine as "theirs" no matter what a maj of people living in Ukraine want or believe. So the entire premise of Putin somehow "needing to save someone" is BULLSHIT.
second, as you noted, old people and children are not "legitimate targets." A putin apologist might (-: say "but the Ukrainian nazis are hiding behind civilians to shoot Russians" but of course if Russia hadn't invaded they wouldn't be shot.
Essentially, Putin's destroyed what little credibility he ever had in asserting some Ukrainians in Donbass and Crimea wanted to have closer ties to Moscow than Kiev. ..... Because he is killing people who never did harm to anyone to achieve control of all of Ukraine.