The medical establishment claims that we get slower both physically and mentally as we get older, but I'm not buying it! I personally believe that time itself is accelerating while we stay the same, giving the illusion that we are slower. I call this my theory of temporal relativity!

Hey, we already know that time is malleable, aka the "photon in a box" experiment, so why not?

On a slightly more serious note: I solved my "am I slower" anxieties by simply never knowing how fast I was/am, in the first place. No cycle computer, and no GPS. I don't even know how far I've gone, except by mapping it out on google maps afterwards.