I think you're mistaken "amusing" for amazing.
The Stones' drummer has been famous as a drummer all his life. When we see him perform what is, really, a feat of physical dexterity and stamina as well as musical virtuosity, we superimpose upon him the image of all those young men and incrementally older men we've seen him as over the years.
Human perception is only sensitive to differences, not absolutes. Gradual change does not strike us as remarkable, even if, gradually and over time, great change is effected.
On the other hand, due to the sheer physicality of drumming, the majority of drummers we've seen in our days are young. At 42, I struggle with physical tasks that were easier when I was 18. This process will not reverse itself.
Projected on our minds' cave-walls, then, when we picture a "typical" drummer, is a young person. When this amazing woman walks into frame, she is vastly different from that picture. Our sensitivity to relative differences is triggered by that wide gap, causing a moment of delightful surprise.
A person who has grown old without losing the stamina and dexterity necessary to accomplish the virtuoso sprint represented by a drum solo isn't a figure of fun, she is a figure of inspiration. She is a reminder to all of us that artistic talent and physical ability can be decoupled, but that artists who are lucky and who are diligent and who are clever can find ways around the insults of age to accomplish feats that shame youth.
As Ciardi wrote: "The old crow is getting slow/the young crow is not... The only thing the young crow does not know/Is where to go."