David Sinclair is a Harvard researcher who believes aging is a treatable disease. His book is called "Lifespan: Why We Age and Why We Don't Have To".David Sinclair is a Harvard researcher who believes aging is a treatable disease. His book is called "Lifespan: Why We Age and Why We Don't Have To".David Sinclair is a Harvard researcher who believes aging is a treatable disease. His book is called "Lifespan: Why We Age and Why We Don't Have To".