My guess is that the mental, physical and emotional effort needed would at least equal that of a pianist with a focal dystonia attempting to recover a previously brilliant technique. However, for a late starter, all the mental and physical pathways would have to be wired from scratch, as there would be no memory of past sensations to aid the process. But just as people have fought and recovered from dystonias, so we must not rule out the late starting virtuoso. It is just that the struggle is immense, requiring unceasing, almost manic determination over several years, and the life regimen and responsibilities of most older people probably imply a prohibitive time limitation. Nonetheless, I would like to think that somebody of independent means and plenty of free time could do it.