Blue zones, places where a high proportion of people who live to be over 100 years of age, have been examined and analysed for variations in diet, level of education, physical activity, proximity to water, trees, etc, etc, etc.

It turns out that what they all have in common is poor or non-existent birth records, and high incentive (eg pension entitlements) to lie about their age.

Netflix - Secrets of the Blue Zones
Netflix series Secrets of the Blue Zones

Despite Netflix, it turns out the only secret of the blue zones is this: lie about your age.