What follows is based on a single biographer's account, not serious research.
Florence Nightingale was a fascinating lady: intensely depressed; she heard voices; she hallucinated; she determined that she had a calling in life but it took her a number of years to decide that that was nursing (which at the time was unheard of for an aristocratic lady, and for good reasons) and every time she determined to leave home to attend the nursing school in Germany, members of her family said, “Oh, how can you leave us! Bring me my smelling salts – I shall faint!” and she relented and stayed.
Meanwhile, she wrote to hospitals around Europe requesting information on medical care, and stored the papers in her room in her parents' house, taking particular delight in the statistics.
The man she wanted to marry proposed to her; but she turned him down in the idea that he would interfere with her nursing work. This at a time when she had neither received training in nursing nor done any.
She was miserable and kept hallucinating because she felt that she ought to be nursing but could not bring herself to do it.
Finally, when she was thirty, she took the initiative to leave home and go to nursing school.
When she came home from the school, she took charge of a London hospital; then the government heard about her expertise and sent her to the Crimea organize the military hospitals there.
When the Crimean War ended she came back to England and spent the rest of her life organizing British, Canadian, and American hospitals. She is evidently responsible for modern medical care as we know it.
Cecil Woodham-Smith says (in a different biography) that the Crimean War produced two geniuses: the engineer who designed the Russian defenses at Sebastopol, and Florence Nightingale.
I thought that was a very impressive story.
I think it's fascinating that she carried her life in a box for thirty years before finally taking the lid off, and then turned out to be a genius.
The moral I take out of the story of Florence Nightingale is: if you know what you should be doing, do it; don't wait thirty years...!