Every time our cells divide, there is a possibility for error. The older we get, the more cell divisions and more errors. Cells also have some ability to correct some errors, but these abilities fade with age. While we may develop some incremental methods of improving cell division accuracy, there are too many factors involved for a single magic potion to cover them all. Our bodies are also storehouses for toxins and less than desirable by-products from ordinary organic functions. These are so numerous, that it would take many therapies to remove or neutralize them. We also suffer from inumerable injuries during a lifetime, ranging from the "too small to notice" variety, to the severe; all of which our bodies repair imperfectly. The longer we live, the more injuries we accumulate.
My guess is that electo-mechanical solutions will arrive first since a single replacement part may correct any number of organic defects.