I suspect it’s mothers/grandmothers.
The cellular machinery (mitochondria, etc) come from the egg, not the sperm.
Two experiments I wonder about would be:
Take an egg (like a mouse egg) and inject it with a mix of other germ lines mitochondria. Fertilize and watch the lifespan.
In one of the higher primates, re-introduce the third gene needed for Vitamin C synthesis. Most animals on the planet make their own Vit C, but humans, fruit bats, a few others have suffered the mutation of losing that gene.
It would be interesting!
Children of teenaged mothers have the highest death rate, which falls as the mother matures. If the child’s grandmother is around to help and teach, the survival rate of the children improves. An active grandmother statistically means more surviving grandchildren.