A new experiment seems to provide prove, at least in principle, that gene therapy on adult animals can extend slow the effects of aging and significantly extend individual health and life. Via Science Daily:
A number of studies have shown that it is possible to lengthen the average life of individuals of many species, including mammals, by acting on specific genes. To date, however, this has meant altering the animals' genes permanently from the embryonic stage -- an approach impracticable in humans. Researchers at the Spanish National Cancer Research Centre (CNIO), led by its director María Blasco, have demonstrated that the mouse lifespan can be extended by the application in adult life of a single treatment acting directly on the animal's genes. And they have done so using gene therapy, a strategy never before employed to combat aging. The therapy has been found to be safe and effective in mice.
...Mice treated at the age of one lived longer by 24% on average, and those treated at the age of two, by 13%. The therapy, furthermore, produced an appreciable improvement in the animals' health, delaying the onset of age-‐related diseases -- like osteoporosis and insulin resistance -- and achieving improved readings on aging indicators like neuromuscular coordination.