verse - First, the quote was "28 - 34 was prime". Secondly, Ewing peaked at 28. That's 1 year in the range and the rest drop off rapidly. Robinson had 2 spikes and after 30 fell off dramatically. My point that you must have missed is that for most NBA players not named Olajuwon, 28 is close to peak....not 28 thru 34.
The better question would be to ask how high will Yaos PER be in his prime. Its a hell of alot more accurate than trying to guess his specific stats Id say a PER of 28 is very attainable and would be among the highest a Center has ever put up. A PER of 30 would be Shaq-Esque
Statistically centers do seem to peek about 28 (Jabbar peaked very early). But there is more to the game than statistics, and many of the top centers continued to improve or play as well as they did at 28 beyond that age. Hakeem continued to improve after 28 not because his skills got so much better, but because he became a smarter player. I think Yao is just entering his prime. Whether he will improve much statistically is hard to say, but I think because of where he came from his opportunity to continue to improve for years may make him an exception. Is there any trend to the ages of the top centers when they won their rings in their career?