Fish's ascendancy over the past two years is not from late blooming/lower mileage. He has blossomed due to a commitment to vastly improved physical conditioning and a mental strength from being very comfortable in his personal life. He had the talent but just wasn't applying it. I remember seeing him in a lunch shop in Tallahassee during the '06 Challenger there. That was in the era of his initial rededication. IIRC, he won that week and began a push to get back to ATP level. Five years of hard work is not a "low-mileage" existence.
Fish is 29 and turned pro in 2000. He's played around 450 matches.
To contrast with a comparable early bloomer, take David Nalbandian. Also 29, also turned pro in 2000. He's played over 500 matches, despite being injury riddled for most of the past 3 years and seldom playing anything close to a full schedule in that time.
Hewitt's even worse - he has over 700 matches on the clock, despite being only a few months older and having barely played in the last two years.
Like it or not, the guys who deliver early put their bodies under far more strain far earlier due to constantly playing the top guys and going deep into tournaments. As a result, once they become really experienced, mature touring pros their bodies are shot. Sure, a lot of Fish's current success has to do with how he's remodelled his game. But a lot of it also has to do with his age and experience level compared to a lot of the other guys around him. It gives him a big advantage.
Look at all his contemporaries whose bodies have fallen apart due to the strain of modern tennis. Do you really think he'd be ahead of them if they were still kicking around injury free? And do you really think that Fish would still be performing the way he is currently, injury free, if he'd remodelled his game 8 years ago?
