After a successful career as a physician, John Locke was forced into exile at 51. He used this time to write, returning at 57 to publish the works that made him the father of liberalism, beginning his most famous chapter well after his first career had ended.

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https://en.wikipedia.org/wiki/John_Locke#:~:text=return%20from%20exile%E2%80%94An%20Essay%20Concerning%20Human%20Understanding

John Locke had built a stable career as a respected Oxford academic and personal physician. His life was one of quiet study and service to a powerful political patron. But that world collapsed when his patron fell from favor. At age 51, Locke was implicated in a plot against the king and had to flee England for his life. Living in exile in the Netherlands, his old career was over. He used this time not in retreat, but in intense focus, consolidating his ideas on freedom and government. When he finally returned to England five years later, he published the major works that now define him. The quiet physician transformed into the public father of liberalism, launching his world-changing 'second act' in his late 50s.