If slowing the aging process is what you want, and if you are going to choose a doctor to help you, I suggest that you ask that doctor's age, then step back and take a long look at that person. If this person is not looking a lot younger than the stated age, look elsewhere for someone who knows and practices the information of anti-aging. From a species survival standpoint, that is what your body is for. After age forty, nature doesn't give a rip about you, because you have lived long enough to have fulfilled your reproductive purposes. This is true throughout the animal kingdom.
Many species die immediately after having laid the egg, fertilized the eggs, given birth, etc.
From an evolutionary standpoint, it is no surprise we grow old. Nature wants us out of the way, so there will be room for the next generations. The body doesn't have the courtesy to break down all at once, it goes down the drain system by system. This gives us the opportunity to deal with it and repair each breakdown as it happens or, better yet, prevent it before it happens. After accounting for the ill effects of a poor diet and lack of exercise, the manner in which the body deteriorates can be traced to the failure of the endocrine and exocrine glands.