Because for it to qualify as a cure it must be mass producible. If it only works on one person, you haven't cured aging, you've merely repaired a body.
Realistically though, we have a pretty good idea of what we're looking for. We don't know the exact combination of chemicals that cures aging, but we know it's going to be a combination of chemicals, and we know we can mass produce those.
Realistically though, we have a pretty good idea of what we're looking for. We don't know the exact combination of chemicals that cures aging, but we know it's going to be a combination of chemicals, and we know we can mass produce those.