In Book IV of The Iliad, there's a part where King Agamemnon is going through the soldiers and talking to everybody. He speaks to Nestor at one point:
He passed on to Nestor, and found him among his Pylians [...].
The old man had seen war before, and he knew all about it. Agamemnon was glad, and he told him plainly how he felt:
"You may be old, sir, but I only wish your knees were as nimble and your strength as firm as the temper in that heart of yours! Ah, well, such is life. Old age is old age. I only wish others were old and you were young!"
The old hero loved a good horse; and he answered:
"Ah, your Grace! I do wish indeed I were now as young as I was when I killed Ereuthalion! [...]"
(translation by W.H.D. Rouse, 1938)
What does the line "The old hero loved a good horse" have to do with any of the context here? How is this related to the matter of Nestor being old?