I would say Heterochronic parabiosis. Basically, a young person and an old person share a circulatory system. This means that the factors which make a person young get into the old person along with the dilution of factors which make a person old. One could possibly have young people feed their plasma into the old person to rejuvenate them.
As well, senolytics may be useful, clearing out damaged cells and the factors that they circulate which make people old. See here.
Edit: Heterochronic parabiosis is the procedure of surgically joining two organisms of different ages so that they share a similar circulatory system. Because aging is a systemic disease (it affects all parts), a significant percentage of the factors which govern again are quite often found in one's circulatory system. There are factors which rejuvenate people and keep them young and their are factors which contribute to aging. By linking circulatory systems, the old people get the 'youth' factors, while offloading the 'aging' factors onto the young organism. This leads to the old organism rejuvenating (though it must be said that the young organism gets the short straw as it ages). So inserting blood plasma from younger people -- which some researchers are currently testing or about to test -- may be a way to get a young person old again.
Senescent cells also influence aging. These cells are cells that are dysfunctional but have not been cleared through apoptosis (cell death). They exist in a senescent state where they give off aging factors into the local environment and blood stream. Removing these cells through various chemicals called senolytics has been shown to increase cardiac output and reverse other signs of aging in mice. One could imagine that a person may be given senolytic compounds to rejuvenate them.
Edit 2: I also want to say that one could potentially isolate the factors that make organisms young and basically have a drug cocktail. Such factors like GDF11 show promise to do so. The problem is that there are so many factors which govern aging and youth so coming up with a complete list is very hard and very tricky. You can though, dependent upon how technical you need it to be, say something like 'a drug cocktail to extend aging which included GDF11, blah, and blah.'