As the global population of nonagenarians swells toward an estimated 230 million by century's end, a UC Davis and Kaiser Permanente study offers the first substantial evidence that the inequalities shaping dementia risk in middle age do not dissolve with extreme longevity — they endure. Tracking over 800 diverse adults aged 90 and older since 2018, researchers found that women, Black participants, and Hispanic participants carry disproportionately higher dementia burdens even in the tenth decade of life, while a single gene variant can either halve or double one's risk depending on gender and