Do you think that a person's age and the amount they eat each day are basically in proportion

Yes, inversely. Younger people need more food to grow up into adulthood. Babies and teenagers eat the most because this is the most rapid period of growth. Babies eat a lot to grow into childhood and teenagers eat a lot during puberty to grow into adulthood. However as you get older, you stop growing and do the opposite, requiring less nutrients as your body slowly decays.