Mikhail Chigorin apparently learned the rules of chess at 16, but only really started playing at 27.
Gersz Salwe started playing around age 20, and apparently entered his first tournament at 36.
And in terms of blooming late, Oscar Shapiro and Bernard Friend became GMs in their 70s.
(Also, I don't see it stated anywhere that the prisoner was not an exceptionally-talented youth.)
Mostly, I think, because becoming a GM is a full-time job and you don't earn any money while doing it.
You need to go to a lot of tournaments around the world, continuously study to get prepared for opponents, and have enough money to fund it all.
So, you really have to want it as an adult and have nothing else that you would prefer to do.
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.