From what I read on this debate, I think that people should be careful that the debate is not so much youngsters (teens are mentioned here for instance) vs oldies (>=30 years old),
but rather youngsters vs players with an "average age" (24-28)
Not sure. Players 24-28 are usually at their best and if they outperform younger ones, that's pretty much expected. However, people speak about stamina and endurance and then you have Haas and Stepanek who are both nearly 35 and doing much better than most if not all of 'youngsters'.