Age is defined as the length of time a person has lived or a thing has existed. Then what does age have to do with mental and physical degeneration other than what you believe it does? I think that what you believe about the aging process has more impact on the way you age than genetics. You simply become what you believe.
In my profession as a personal trainer for over 20 years, I have noticed that people who have a positive mental attitude about aging are the ones who become ageless. You never hear them complain about growing old and consequently they stay healthy and strong throughout their lives. On the other hand, the people who complain about the aches and pains of aging seem to attract the very conditions they speak of into their lives as they get older. This leads me to believe that the mental and physical decline associated with the aging process is mostly about how you think about getting older.
Every cell in your body is replaced and renewed every 11 months. That means you have a completely new body every year. I believe whether your body is renewed with strong and healthy cells or with weak and unhealthy cells is all in the way you think about aging.
My grandmother was 92 years of age when she passed from this earth. I never remember her being ill a day in her life other than a common cold every now and then. She remained mentally sharp and physically fit throughout her entire life and I never heard her complain about getting old. That's a testament to the effect that a positive mental attitude has on aging.