The age of your skin should be judged based on biological factors rather than simply your date of birth. Biological and chronological age rarely very far apart but they are not the same. The rate of aging varies among people due to genetic and lifestyle differences.
The variation in the rate of skin aging is particularly high (compared to other tissues) because the skin is more exposed to the environment. When optimizing your skin care, you can use your chronological age as a starting point but you should also take into account biological factors that may have affected your rate of aging.
For example, if you are in your twenties but your skin has suffered a lot of sun damage, you may benefit from the anti-wrinkle treatments (e.g. tretinoin a.k.a. Retin A) that are otherwise best used later in life. If you are undergoing early menopause in your late thirties, you might benefit from topical estrogens and/or progesterone even though such treatment are typically contemplated in late forties.
