well I am 55 and do not have any sagging skin at all.
However, the length of time required to reduce or eliminate sagging skin will largely depend on its severity to begin with.
A reducing diet for weight-loss will produce sagging skin, but water/dry-fasting has a habit of "tightening" the skin along with the reduction of excess weight. Post-fast exercise also has a rejuvenating effect on the skin as well, and in particular, rebound exercise is strongly recommended.
53 is not considered to be too old, where repair of any of the bodily organs is beyond redemption.......far from it: you are 53 years young.
Perhaps some of the members could vouch for this and I am thinking of Mouseclick in particular, who may wish to reply here.