I agree, this is one of the biggest flaws with this line of reasoning. However, it does say something (although it's unclear what it means for us) that some of those cultures had less incidence of the diseases commonly associated with old age compared with nearby similar cultures that ate less or no meat.

> Older cultures also didn't live to their 70s like we do now

This isn't exactly true. There has never been much of a shortage of 75 year olds, excepting certain grindingly poor societies.