The Old Took was Thain of the Shire for seventy-two years, so that his eldest son Isengrim was eighty-eight when he inherited the title. Due to his great age, Isengrim was Thain for just ten years, and was succeeded by his younger brother, who became Thain Isumbras IV. Isumbras was ninety-two years old when he inherited the title, and his Thainship was even shorter than his brother's - after nine years, he died, and was succeeded by his son Fortinbras.
Notes
1
'Iron arm' is the literal meaning of the name Isumbras, but Tolkien almost certainly took the name from 'Sir Isumbras', a popular figure in medieval tales.