About 15 years ago this forum's parent site Hockey's future also focused on prospects and they graded them: 8 was basically a career 1st liner or a top-2 defenseman, 9 was an elite player (they used to name examples like Yzerman, Hasek, Roy, Lidstöm, Forsberg, Sakic, etc). They used to call 10 a "generational talent" - they defined it as "a player who is head and shoulders above their peers and change they way the game is played". They listed examples as Gretzky, Lemieux and Orr and there was also a phrase like "maybe Sidney Crosby, but we'll see". They also added accuracies on prospects, A meaning player will reach this level, B at least one level below, etc.
They didn't hand out this title to everyone like the case is today on this forum. As I recall Crosby was a 10C, meaning he could reach the Gretzky/Lemieux level but he would at least be a 1st liner (10C = 10-2=8) for his whole career. Ovechkin was 9A (9-0=9) - he was basically gonna reach the Yzerman/Forsberg/Sakic level but his game lacked the wow-factor which would make him considered really special.
To conclude, hockeysfuture.com was the first place I ever saw the term "generational talent" being mentioned and they actually did define it.
As my personal note I would add that if a person has a really special talent in anything - music, math or hockey - it is obvious already when the person is a 7 year old. That was the case with Gretzky, Lemieux and Orr. You don't all of a sudden develop that special ability. You may become really good but that extra special ingredient will always be missing. If Cale Makar had this ingredient he would not drop to 4th overall in the draft and we would have seen HNIC specials about him 5 years before his draft.