It's plenty possible, but few have the desire to put in that much work as they get older. There are people who play at near-GM-level strength in tournaments ref

It's plenty possible, but few have the desire to put in that much work as they get older. There are people who play at near-GM-level strength in tournaments reflected in their single tournament evaluations, but don't play enough to obtain 2500+ rating or score enough GM norms in major tournaments. There's a even a guy from Russia who is 2550ish rating and isn't even an IM because he hasn't scored enough norms, and is 3000+ bullet/blitz on Chesscom, which is incredibly elite. Someone picking up chess at age 25 could certainly become a GM. They just usually don't have the desire for it.