Did Yamamoto die of old age or was he killed?
He is both subject to senescence and subject to death. If he is subject to both, he can die of old age.
1+1=2 mate.
Immortality does not equal invincibility.
This is true but probably not for the reason you think. Invincible means "unable to be conquered or overcome". Vincible means "able to be conquered or overcome". It comes from the word
vincere, meaning "to overcome".
In short, invincible would be "not subject to defeat".
For example, trapping something is defeating it without needing to kill or even harm it. A being that is "not subject to death" can still be "subject to defeat". Think of the
Mafūba from Dragon Ball.
I assume you meant invulnerable meaning "not subject to damage".
Just like when you were talking about immortality (not subject to death), you actually meant biological immortality (not subject to senescence).
Tis pretty funny to see you criticise the reading ability of others when you are clearly not understanding the meaning of individual words or phrases this much.
rapid aging which is not a natural occurrence amongst shinigami as a whole.
Ageing is. We see it.
We literally see Soul Reapers age. Gin used to be a small kid, now he's an adult. Ukitake used to be a kid, one that was nearly killed by an illness he still suffers from. Yamamato used to be middle aged, now he's an octogenarian looking sassenach.
We clearly see these sods age. They just age slower than regular humans.