I think six pack abs are definitely possible at 55+ with an ever increasing amount of determination and effort. For Arnold Schwarzenegger, he finally accepted defeat at age 72 but is probably one in a billion.
As a college athlete I was 5'10", 165lbs, 11% body fat. Pretty well ripped at that point.
Today at 69, 5'10, 185. I am a lot softer now but not too portly. My vitals are good, energy good, zero health issues, no pharma. Reasonable activity level but not training daily. Doc says I am in pretty good shape for being as old as dirt.
Back when dinosaurs roamed:
