Hmm I don't know. In my culture (which was a tribal one not too long ago) the emphasis was more on 'skin groups', ie avoiding interbreeding, not banging as many babies as we could out of the oldest mums in the village.
Generally, our elders would have a hand in raising all the children, not just their genetic offspring, this way skills were passed on to all.
Realistically, mothers rarely reproduced past late 30's early 40's in a tribal society, it was just too dangerous healthwise for mother and baby. The skills that a 40 year old woman had developed over her years were just too valuable to the tribe to warrant risking her life making a baby.