[troad]

Isn't that conceptually incoherent?

Premise: Thinking slower makes time appear to pass faster, and thinking faster makes time appear to pass slower. (Per the two paras following "Consider")

Thesis: The secret to living longer is to alter one's perception of time, by thinking slower.

But given the premise, thinking slower would make appear to pass faster. Ergo, it would make life feel shorter, not longer.

In fact, the premise actually supports the exact opposite thesis: that the secret to long life is to think as fast as possible.