Your metabolism is bespoke to you!
Your metabolism is made up of a myriad of factors i.e. height, weight, age, muscle mass. Your metabolism is a fixed point and the only factors that can effect changing it are an increase in muscle mass (which only increases it by a very tiny margin) or a disease like PCOS.
So if you are a tall, young male with a lot of muscle mass your metabolic rate is going to be higher than a short, elderly lady’s with PCOS.
Where people get confused is that they incorporate physical activity as part of metabolism. These are two separate things. Your calorie expenditure is made up from your BMR/RMR + your physical activity.
Calories expended from physical activity is something you can very much adjust. Exercise, walking, gardening, swimming are just some of the ways you can expend calories. The more you do of these activities the more calories you burn and if you are burning more calories than you are consuming, you are losing body fat!
Two people of the same age, weight, height and muscle mass and sex can have very different calorie expenditure rates, if one of them is very active (lots of dog walking, physical job, exercise) and the other is very inactive (no exercise, sedentary job).
Your metabolism + your physical activity = energy/calorie expenditure.
