Unexpected. They keep saying that in the last 10 years it's been harder than ever for teenagers and other young guns to break into the top levels, since fitness is more important than ever. But based on this, it's probably just the emergence of teenage breakout champions (like Becker, back in the day) that's been curtailed. The average age of top 10 players hasn't changed much.
Yes, I mean usually guys like Berdych or Raonic have been part of the Top 10, or even a regular Lendl or Roger. Note: I mean Lendl and Roger entered the Top 10 in a more "normal age" 20-21
But the 'distortion' was made for those who made also huge history by having a super early breakthrough, call it Becker, Borg, Mc Enroe, Chang, Agassi, or a bit more recent with Hewitt (youngest #1) Nadal, Murray and Djokovic. And it is quite logical that those big name stayed for a veeeery long time. Connors was -with the exception of 1 week- a top 10 until almost 37! Agassi later and now Roger and David F. are taking that average up. Yes, it is a bit sad for the likes of Berdych, Raonic or Nishikori or even Del Potro to have emerged by almost the same time the best player ever, the best ever on clay, Nole (who has some more room to make history) and Andy.