This has been discussed a lot before. The age rating that the game gives to your characters is an indication of their age, something like the test you can do in RL to see how your life style has affected your relative age. It isn't a direct age for your character, since things like wounding etc speed up the aging process.
i.e. if your character is classified as "80 years old", you can expect him to have difficulty walking fast and to need a nap in the afternoon. This can be either because he has actually lived for 80 years, or that counting his scars in the morning takes 3 hours each day (and he has to recount them, his long-term memory is toast).
