Used to emphasize someone's healthy state, both physically and mentally. He's been jogging daily and is in fine fettle for his age.
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British Usage
Particularly common in British English, not widely used in American English. You'll hear 'in fine fettle' often when talking to British friends about health.
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Positive Connotation
Expresses a positive opinion about someone's condition or spirits. After her vacation, she returned in fine fettle, ready to work.