The chronological age is the age of the calendar.
Metabolic age is generated by habits.
Have you ever said or heard: -tenes 40? ... you look like 30! - Healthy habits do that in your metabolism; and therefore, in your physical state.
Metabolic age is what you can do differently to two people born in the same year, if one has maintained healthy life habits and the other has not.
Metabolic age is a calculation between weight, fat, age and sex that some professionals use when preparing the nutritional assessment of a patient. This element tries to mention the "real" age of the body, and can be very different from the chronological age.
There are many formulas, you can even get the data through the famous Bioimpedance scales ... but, do not confess. All formulas have their limitations and lack scientific evidence. They only help to "estimate". The most important thing is how you look and how you feel.
Try to invest time in healthier habits through nutrition, physical activity and rest to improve your metabolic age.