Whey has huge problems that are absent from other protein sources. Similarly, something like pure egg whites (minus the yolks) would also generally be a bad idea. Although there are various pros and cons of high and low protein diets, the least you could do is use an alternative to whey such as casein, gelatin, casein + gelatin, or more whole foods. Even adding in some cocoa powder helps in spite of it being an unrealistic main protein source, as the amino acid profile is unique. Lowish protein diets are one of the ideas consistently yielding positive results in longevity experiments, but such diets have variable practicality, especially in athletes and weightlifters. The answer, I think, is to keep seeking ideal amino acid ratios, as some of the primary mechanisms of action in low protein diets promoting longevity are thought to be methionine and tryptophan restriction. Glycine supplementation has been shown to mimic the effects of methionine restriction, so I think seeking protein quality is likely to yield the best results without risking starvation.