Just one guy won at 36...and he won his first at 21 which isn't that old. There was a time in the 80s when 17-18 was a normal age and that's gone, but overall I don't think the ages have gone up by that much.Today 25 is young. Just think we have "boys" winning slams regularly at 36, impossible 20-30 years ago, as it will be vary rare from now on to win a slam before say....23-24. Look at Zvev, he is just not built enough to taky 7 BO5 matches in a row.
The average peak age today has shifted from 18-23 to 25-30. And today after 30, you still improve tecnically.