Gerontologists have started using the term "super ager" to describe these smarty-pants seniors. The National Institutes of Health even uses that term on its webpage: old people who "perform demonstrably better on memory tests". How can you be one of these super agers? Like much having to do with the brain it comes down to three factors:
Super-agers don’t have dementia, they don’t have MCI, and they don’t even have "normal" loss of cognitive function.
Podcast with neuroscientist Emily Rogalski about Superaging: https://www.navneuro.com/66
While most uses of "superager" refer to maintaining intelligence. But there is also the concept of physical superager - people whose bodies don't decline in capability much. There are many metrics: grip strength, aerobic capacity, bone density.