Former Northwestern University swimmer Richard T. Abrahams became the first 50-year-old to break 50 seconds in the 100-yard free-style. His time at age 50 was faster than when he competed at the 1964 Olympic Trials.
A decade later, in 2005, Abrahams became the first 60-year-old to break 50 seconds in 100-yard free-style. His best time during those intervening 10 years actually slowed by only 0.34 seconds.
To swim 100 yards under 50 seconds requires a lot of explosive power and endurance in speed, skills we are suppose to loose firs when we age. But apparently with a proper strength and speed training it is reversible.
My personal best for 100-yard free is 1 min 11 seconds. I guess I have to practice a lot to keep up with some 60 year old guys who are much faster and stronger than me.