If hunters had a high mortality rate, then I would guess that a lot of older widows would have little choice but to breed with the younger boys of the tribe.
If I remember correctly, Gengis Khan’s wife was 5 or 6 years older. It makes sense. Young men are at the peak of their strength and energy for hunting and fighting. Women their age are not fully mature for childbearing in what was a very hard life for women as well. So it would make sense to have an older more physically mature woman for a mate. If Neanderthals were men at age 13, that would have been a bit young for the childbearing female.