The only strictly genetic component to an “increased” metabolism is the amount of “Uncoupling Protein” you have on the inner cell membrane of your mitochondria. The more of this protein you have, the less efficient your body is at turning calories into energy so to speak. The calories are just turned into heat energy. This requires more calories to support body function.
A high concentration of these mitochondria with a high levels of UCP are located within what’s called brown fat. This brown fat is strictly used to generate and maintain body heat. The amount of brown fat that you have decreases with age, contributing to 90 y/o men wearing cardigans in the summer and a slower “metabolism.”
Also, the “eat smaller meals more frequently” is actually a fallacy. Much like “always eat breakfast,” it becomes a self-fulfilling prophecy. Healthy people hear it’s healthy, attach themselves to the habit, and it becomes consequentially associated with health.