Even reversing aging would presumably take a not-insignificant portion of a person's life span. If the rate were magically the same as aging, just in reverse, it could take years to notice the difference depending upon your age.
You might examine some of the animal studies for, say, stem cell therapy or senescent cell clearance. Benefits are rapid and very evident for things that do actually work. Even slower items like myostatin blockade to provoke muscle growth show sizable, obvious benefits over a period of a few weeks to a few months.
FTFY