This makes sense, all of their other big time stars which much older.
George Gervin was in his age 21 season when he was traded to the Spurs from the Virginia Squires (when they were in the ABA). Robinson’s rookie year was his age 24 season, Duncan’s rookie year was his age 21 season, Ginobili was 25 as a rookie, and Kawhi was 20 in his rookie year. Duncan and Robinson were 4 year college players, plus Robinson had his obligation to the Navy. Kawhi was a two year college player, and Gervin didn’t start with the Spurs.