Most of Violentlash's deaths have been of old age - nothing unusual considering it ran for 72 years.
I never got the message "died of old age" though, I think. Weird...I was wondering about that.
As far as I know, the game always gives an announcement when a dwarf dies of old age. I've seen it before on the forums, just never in my own forts.
I should also add that this is in v34, where it took 10+ game years to get legendary military dwarves. She was one of the only 3 legendaries I have, so her death leaves my fortress significantly weaker.
Weird. Then it must be changed/bugged in 40.23 / .24, because I know it never gave me that message in Violentlash. Looking at the last picture you also got the message for pets/tamed animals (?), I'm absolutly sure I never got this message for tamed animals - been too long since there were any pets around for me to remember though. They'd also only be announced as dead after some time: most of the time my dwarves carried the corpses of the recently deceased Jabberers to my refuse stockpile, which linked to a minecart which dumped them down a garbage dump to magma level, and the death message would only pop up if I opened up the door to the garbage dump and let a dwarf see the corpses.
The Jabberers (and other tamed animals) must be in a "Schrödinger's cat" kind of state; neither dead nor alive. Because if they'd been alive, they'd not have been carried to the refuse stockpile, but if they'd died, they'd have been announced as dead when found!
It's in
save/[your_fortress_region]/raw/objects/creature_standard.txt -> [CREATURE:DWARF] -> line 198 (at least on my end).
Don't really see the point in it though, to actually have dwarves die of old age in bigger numbers you have to play for a VERY long time. Of Violentlash's original 7 only one has died after 72 years after embarking...but to each their own.
And it should work post world gen. Turning the goblin need for food (and water) off again worked as well after world gen.