He separates just a handful genes (of 20,000 + total) which govern aging mechanism in the living beings not just humans. He proves that triggering those genes (either on or off) can alter lifespan in rats. He takes twin rats who have similar sets of genes and shows that they age differently with his experiments in the lab.
These genes can be triggered naturally by making fewer adjustments in our lifestyles which are known to benefit from forgotten times but this research only enforces it. They are:
a. Regular Exercise and Intermittent fasting
b. Sweating out occasionally and also taking cold showers exposing our bodies to thermal shocks which it can bear without permanent damage
With intermittent fasting, idea is not to starve your body of nutrients but to trigger the internal repair mechanism which aids in expanding the lifespan. Skipping a meal a day or fasting couple of days every few months (whatever works for you) would reverse the aging process with biological functions getting triggered that may result in you looking younger than your age. Instead we supply meals to our bodies at such a regularity, our bodies become complacent and the repair mechanism at cellular level gets shutdown and we begin to age. Similar effects are produced by exposing ourselves to milder thermal shocks. Apart from this, author also suggests consuming fewer supplements to help reverse the aging process further.
The book is more of a scientific read and if the reader has good knowledge of cellular biology and a good knowledge of genetics, he or she would appreciate it more.
Remember this author will give more years to your life but adding life to those extra years is up to you.