Agree with Jim G that the general trend is research indicating lower, rather than higher protein, being linked with longevity (see review paper further below). Worth mentioning also are the Blue Zones (five populations that have the highest lifespan and, importantly, healthspan). One of them (can't remember which) had 10 times the rate of people living to 100 compared to the US (and not genetics as the effect disappears on migration).
When they looked at what these five populations ate, as well as high complex carbs (65%) and 95% plants, it was also low in protein (15%). The nice thing about the Blue Zones is that National Geographic initially just sought to find the longest lived populations worldwide. The fact that all these populations happened to have a similar dietary pattern overall would seem to be very supportive that it is the most longevity promoting.
Review article mentioned: The impact of dietary protein intake on longevity and metabolic health
"Lifespan and metabolic health are influenced by dietary nutrients. Recent studies show that a reduced protein intake or low-protein/high-carbohydrate diet plays a critical role in longevity/metabolic health. Additionally, specific amino acids (AAs), including methionine or branched-chain AAs (BCAAs), are associated with the regulation of lifespan/ageing and metabolism through multiple mechanisms. Therefore, methionine or BCAAs restriction may lead to the benefits on longevity/metabolic health. Moreover, epidemiological studies show that a high intake of animal protein, particularly red meat, which contains high levels of methionine and BCAAs, may be related to the promotion of age-related diseases. Therefore, a low animal protein diet, particularly a diet low in red meat, may provide health benefits. However, malnutrition, including sarcopenia/frailty due to inadequate protein intake, is harmful to longevity/metabolic health. Therefore, further study is necessary to elucidate the specific restriction levels of individual AAs that are most effective for longevity/metabolic health in humans."
Interesting in that it seems specific amino acids are important. A bit of a write up on methionine:
https://medium.com/@llicit/a-potential-key-regulator-of-ageing-93ef308a0707
