While that claim probably sounds staggeringly presumptuous, my definition of "best", unlike one that applies to, say, Michael Phelps, doesn't hinge on how fast I swim. Instead I mean that, among the billions in the human race, there are perhaps only a hundred or so swimmers on earth who use their available energy and power as efficiently as I do, who enjoy every stroke as fully and who practice effectively enough to keep improving continuously.
It's that last definition of "best" that excites me most. There's a Japanese term "kaizen" which means continuous improvement; specifically it infers "incremental improvement through cleverness, patience and diligence." At age 54, I feel I'm the embodiment of Kaizen Swimming. After 39 years of swimming, coaching and teaching, after over 15 million meters of swimming (I average about 500,000 meters per year), I'm still making regular advances in my control, efficiency and ease. I also swim 1500 meters faster than I did as an 18-year old college freshman in 1969.
In May 2003, while filming a Total Immersion video in Santa Barbara, California, and training with the Santa Barbara Masters in their 50-meter pool, I swam a series of 20 x 50, interspersed with 10 x 100. (If you train in a 50-meter pool, you can compare your counts with mine.) On the 50s, I averaged 30 strokes per length. Two years earlier, it required intense concentration and all the perfection I could summon up to swim a single 50-meter lap in 30 strokes—and about 50 seconds. During that set I did several as fast as 44 seconds and all 20 in 48 seconds or less.
Swimming Harder Doesn't Help
Because I'm a Kaizen Swimmer, even after 38 years of practice, I still think of myself as a "Developing Swimmer", a category that every triathlete on earth would do well to embrace (yes, even those who may have swum competitively for many years and even those who swam on the national level.) So long as you have human DNA, and haven't somehow acquired fish DNA, I guarantee you can continue to improve as a swimmer. Even at age 54 or 64 or 74. And here's the key lesson I've learned about improving as a swimmer: Swimming harder doesn't help.
The only time my swimming stagnated was my final two years of college, when I believed that working hard was the way to success. From the time I began swimming as a high school sophomore through my college years, I prided myself on working harder than anyone else in the pool and, for a few years, I improved steadily. I also swam an average of 40,000 yards per week (compared to 15,000 now) and was a lean and hungry teenager. But in my final two years of college, I continued working hard and actually regressed. In fact it was that frustration as an athlete that led me into coaching.