Seems like pure speculation. There are a thousand different mechanisms that would explain it and would not mean "there is some health benefit". Is there a health benefit of white hair? Of wrinkles? Of ...?

Quite the opposite seems true in fact. Evolution tries make us be on our peak at the reproductive age, and a lot of that happens after is a byproduct/consequence of this, not just for health benefits. Most (all?) of the biological "health indicators" decline after this peak age.