This was too much for Avraham, a hundred years Yitzchaks senior, so he compiled a prayer to the One Hashem. And Hashem saw that it was good, and said, Well you have argues, Avraham. So, we see Avraham asked for age, so that we would be able to tell whom to respect. The Kehilas Yitchak explains that Avraham was not out looking for honor. Rather, he saw a vast potential danger if there was no identifiable way to distinguish between the old and the young.
Older people have more knowledge by virtue of their experience.
As such, they are excellent sources of advice for the younger generation. This is why Avraham prayed to Hashem, and why Hashem agreed. Age was designed as a system by which to readily recognize those who were better sources of advice, because of their wisdom, not just because of their time elapsed, but because of what they had learned in that time. To answer this, we have to look back at the giving of the Torah at Har Sinai as related in Exodus 24. There we see the leaders of the Jewish people standing at the foot of the mountain deriving personal enjoyment from the revelation.