How did Ginrei Kuchiki died?

Ginrei was alive 100 years ago when kisuke was exciled. But now it atleast looks like he died with zanpaku-tô rebelion arc even claiming so (it's a filler so maybe a contradiction)

You can say he died of old age but that doesn't sound right concidering unohana and Yamamoto are alive and kicking and are prolly much older