One concern some people have about bringing aging under medical control is that it might create an immortal Gerontocracy controlling society.
As I discussed in another article, rejuvenation biotechnology would allow older adults to continue working and producing wealth for much longer than they can today, thus benefiting society in many ways.
However, some people are concerned that this might do more harm than good; imagine all those rejuvenated old farts holding onto their jobs forever, preventing the young from getting jobs themselves! Not to mention the risk of a gerontocratic world, where powerful older people get a touch too attached to their chairs, never allowing younger people a chance!