I don't think the joke was intended as an insult to old people or cyclists. It's funny to the average person that doesn't ride a bike or know any older people that do because they see cycling as something far more difficult and/or dangerous than it is.

I suspect most/all of you have had the experience of seeing people be shocked when you tell them you rode fifty or a hundred miles, or you rode so many hundreds of miles in a month, etc. One day I came back from a ride to the Pinnacles (~62 miles RT) and my neighbor asked me where I went. When I told him, he laughed and said "seriously, where did you go?" I'm still not sure if he believed me. To the average non-cyclist that is something that is unachievable for most people let alone someone that is 80.