Ageism is hiring a 25 year old instead of a better qualified 55 year old. It's not "ageism" to say that an 81 year old or a 78 year old might not be able to handle the world's most demanding job.
My dad is 79, and has absolutely energy to do anything, and he's frustrated as to why. My mom is 77, and she's somehow in better health in a lot of ways, but she would pretty quickly loose steam too.