Of course he wasn't talking about reaction time, but it shows an interesting trend. If reaction time slows down, then what else slows down with it? The only reason we accept the reaction time slowdown is because it's easy to measure. What about other attributes which are harder to measure, like general intelligence?
It just seems strange that everyone is saying his assertion is unquestionably false when, if anything, the evidence seems to suggest the opposite.
And don't forget experience, skill, wisdom. You could call those all "knowledge" if you want, but they have more specific connotations than just "knowin' stuff".
I don't disagree that being young confers special advantages and powers. Young people can more easily blunder up a wonderful mistake because they have less to lose. That's important. But that's not the only way!
It just seems strange that everyone is saying his assertion is unquestionably false when, if anything, the evidence seems to suggest the opposite.