為末さんはなぜ23歳以降ベストが出なかったのですか？

I always enjoy reading your posts. I have a question. I apologize if this is incorrect as it's based on Wikipedia information, but I believe Mr. Tamesue's personal best in the 400m hurdles was set in 2001. I wondered why he was never able to break that record in his subsequent competitive career. I imagine he approached the sport with sincerity and implemented creative training methods, so I find it puzzling that he still couldn't improve his record. Is age a major factor? Also, in that case, is his motivation for continuing to compete based more on ranking than on time?