"Negligible senescence" means that you don't get appreciable deterioration with age. You're 240, but you feel 29. EDIT: Ah. They explain that later in the arti

"Negligible senescence" means that you don't get appreciable deterioration with age. You're 240, but you feel 29. EDIT: Ah. They explain that later in the article. That's an unfortunate use of the term, given its history of use in the field.