The only proven way of currently extending life expectancy in a variety of mammals is undernourishment (not malnourishment) but requires further study to see whether it has undesirable side effects.
Long lived species have less response to famine so, according to Aubrey de Grey, not likely to have a big impact in humans.
More info: CR Society International
Low-calorie diet prevents age-related molecular changesMedical Xpress - 25-May-2018
Epigenetic changes strongly influence the way the genes operate. Methylation in humans changes in different areas with age. Harvard Medical School studied methylation in mice as they aged. Changes become more evident at an older age. Long-term low-calorie diet displayed slower age-related changes. Short-term cuts in calories instead made them even faster.
CR Leads to Longer Life but Less Grey MatterGenetic Engineering & Biotechnology News (GEN) - 05-Apr-2018
New study shows caloric restriction in lemurs extended lifespan up to 50%. Grey mouse lemur is a small primate with a lifespan of around 12 years. Fed 30% fewer calories from early adulthood lifespan up by almost 50%. Brain imaging showed a slight loss of grey matter (neuronal cell bodies). However, cognitive and behavioral performances were not modulated.
Reduced-?calorie diet slows ageing in peopleNature - 22-Mar-2018
CALERIE multi-centre trial tested 200 healthy, non-obese adults over 2 years. State-of-the-art metabolic chambers measure oxygen use and CO2 exhalation. Reducing calorie intake by 15% mapped to more energy efficient sleeping. Other clinical measurements were in line with reduced metabolic rate. Evidence that results in other animals can be applied to ourselves.