maybe look at your birth certificate, that should have the information that you are looking for right on it. in todays world everyone needs their birth certificate for all kinds of things from disability claims to getting a social security number or other government ID's (state or country ID, passports, and so on.) so if you cant find yours contact the hospitals records department and your state / county health department.

theres also specialized tests that can tell your treatment providers what your mental age (called mental maturity age) is.

this is what I did when I had problems with trying to figure out my physical age vs my mental age.