Speaking strictly for myself, it would seem that a so-called "generational talent" would be a player of a caliber an observer would only likely encounter once in a single lifetime. (Which is why it's such a ridiculously hyperbolic & grossly-overused "trendy" term.) Someone truly long-in-the-tooth might be lucky enough to see a couple. At sixty-years-old, following the sport since about 1970, I've seen Tom Brady for a long time...and struggle to think of another player who meets the criterion of being head-and-shoulders better & more successful than anyone else playing the game at the same time.