I'm not sure what "conventional wisdom" was upended. Basal metabolic rate doesn't change so much with age, and metabolic rate is largely affected by your weight, muscle mass, and activity.

This stuff is well known in the fitness community, particularly by natural bodybuilders or sports nutritionists. As a small sample of this being well talked about in the fitness world:

https://bodyrecomposition.com/fat-loss/4-determinants-of-met... https://podcasts.apple.com/us/podcast/metabolism-myths-age-s...