Not sure what Thomas Muster's comeback
will be like and I don't know if he will break into the Top 50 next year like 40-year-old Kimiko Date Krumm
did this year on the WTA-tour but it's obvious that players are getting older and older.
There are no teen-sensations at all. Yes, Filip Krajcinovic
reached a semifinal at an ATP-event this year and looks like the next big thing from Serbia but it was not that sensationell that an 18-year-old reaches a semi at a small event. Grigor Dimitrov and Bernard Tomic struggle. Ryan Harris is not there yet.
Fact is, that there is no teen in the Top 100 right now!
The best teen is Federico del Bonis from Argentina - # 148.
Back in the 80ties Chang won his first Slam when he was 17, Becker did too, so Mats Wilander. Sampras at Edberg won their first Slams when they were teens. Then Hewitt was the youngest # 1 ever in the 90ties...
More and more players (like Melzer this year) have their breakthrough when they are almost 30. Most of the successful doubles players are way over 30 (although they still look like college-teens - e.g. the Bryan-brothers).*
This is definitly part of the demographic change.
But also I think that the very young players can't compete with the twens because the game got more and more physical. And the body needs time to develop.
The same on the women's side where players at 14 or 15 used to have their breakthrough in the 80ties and 90ties: Austin, Capriati, Hingis, ...
*By the way: I made a similar thread here a year ago: