I agree, and I think you also see the same with physical health. Our metabolism doesn't actually decline until we're in middle age (nor do you need to ramp up your calories during pregnancy) [1]. The only reason people get fatter over time is because they just keep overeating, and probably get more sedentary over time to boot. Knowing this has really motivated me to build a lifestyle that demands consistent and significant effort that I can sustain throughout my entire life: challenging and diverse mental stimulation, diverse and frequent but low-impact exercise, and lastly, a satisfying and nutritious diet that doesn't cause me to gain weight. It's amazing to learn how strong and durable our bodies are, and inspirational to see how much potential we actually have.
1: https://www.science.org/doi/10.1126/science.abe5017
> [energy expenditure] remains stable in adulthood (20 to 60 years), even during pregnancy; then declines in older adults.