To my knowledge, no pool player ever put his cue down for a few years or more and made a successful comeback at 55 years old.
Joe Balsis, who was possibly the best junior in the world in about 1940 or so, chose not to compete again until the early 1960s, instead working in his family's meat business. He came back at about age 40 and put together a professional resume that would earn him induction into the BCA Hall of Fame. Joe's professional revival at the age of 40 is, perhaps, the most remarkable of which I know.
.... but Johnny is 55, and the deck is stacked heavily against him because of it. Still, there's no need to mock him for taking a shot at a comeback. Hope he can find some of the old magic. In the nine-ball era, Buddy Hall, Efren Reyes, Jose Parica and ageless wonder Ralf Souquet all played great pool at 55, but none of them retired and came back to competition.
Good luck to Johnny in overcoming steep odds to regain top form.