Okay, long winded reading. So the horses that started young won more money, right? What about longevity? They could have raced as 2-3 yo's, run them off their feet then tried to chuck them to a meat factory.
Generally, horses that have raced a long time and stayed sound become great sport horses. But I know that there's a lot of them that started young, raced as 2 yo and then got broken. They may have won some money but now nothin'. you know what I mean?
And oh!  Biggie here.  Most trainers that I hear of will have a late starter for a reason.  The horse started later in life because of conformation/illness/injury.  So they are defective to begin with.

Average, for horses with some experience at this level