If they're gonna police free speech, the least they can do is be consistent about it.
We are all getting older, we have elderly relatives who we love and aging is just an obvious part of life. In that context people won't take it personally and understand the nuance. I can bitch about boomers to my boomer parents without contradiction. And I don't get offended if the kids in my family call me an old person. It is funny because it is so universal.
Obviously that does not justify anything exactly and we should be respectful. But there is good sense in being generous and not taking offence.
My it's just me, but I see "kill yourself" and "kill <other people>" as completely different in terms of severity.
By the way, what kind of person says something like "kill all boomers" repeatedly? Is that supposed to be witty?