Medical science has made no breakthrough that will extend the potential maximum lifespan of human beings. The aging process is a great mystery just like the life itself. What the medical science has achieved is an increase in the average life expectancy, because there are so many fatal diseases that can be cured or prevented. However, this also means that more and more people have to confront the problems of old age, and the problems are undeniable. People would experience physical decline, problems with the social position of old people, etc.
The process by which the protein composing muscle bulk is daily broken down and rebuilt continues throughout life. But with age, muscle tends to deteriorate at a faster rate than it is remade. Age brings a decline in body weight and muscles.
The physical decline of old age is the result not just of the decay of muscles but of a diminished capacity of lungs to take in the oxygen needed to power the muscles. This process starts in the twenties, which explains why a 35 year old athlete, though his muscles may be in just as good a condition as a 25 year old rival, will normally lose in a race. Other bodily changes in the brain, liver, kidneys, uterus, and others, are uncontrollable. The resistance to stress and temperature change is worsen. The brain shrinks.
However, there are ways of ensuring that, physically at least, you can live a more enjoyable old age. The best way that is applicable to everyone, is to do regular exercises. Exercise stimulates the build-up of muscle, even in age.