I think the point is that success in the 12s does not guarrantee success later. BUT if a player is not already a standout by 12 then the chances of being a standout by 18 is very small. There are always exceptions but not many. Most of the stand out players who are not highly ranked at 12 could be if they went the tournament route AND played in their age division. Players like the William sisters played a very limited amount of tournaments and Pete Sampras played up. Agassi played up as well. He was playing in the 12s at 9 and 10.
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