Not true at all. Humans evolved in social groups with complicated cultures and the necessity for significant "group memory". While chance and disease did take some group members out early, elders were generally respected for their wisdom and experience and of course for the labor they could still perform.

Reproducing young has its value when there are no doctors or hospitals, but children take decades to come to full intellectual maturity, to the capabilities necessary to live by brain instead of brawn, and when human labor is the most valuable commodity, that which elders can contribute is still quite valuable.