Interesting chart, which appears, at least implicitly, to define "over the hill" at 50. On 20-mile and longer rides I have lost about 10% of my personal best speed. but so what? At "Beatles' Age" ("When I'm 64"), the game plan is simply to slow the inevitable rate of decline and to live my remaining years to the fullest.
As for speed, I have always been mainly interested in how fast I can climb, and I have never been fast on any sort of descent.
__________________
"Far and away the best prize that life offers is the chance to work hard at work worth doing." --Theodore Roosevelt
Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
Carlton: 1962 Franco Suisse, S/N K7911
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1982 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069