A report from Mr John Gale, known at the end of his life as 'The Father of Canberra' who was noted for his long-lived life and mantle of being the oldest journalist, coroner and author in the world. So it is of no surprise to me that he would also know the oldest horse in the world and a horse that worked till the day that it died.
Whether it was indeed the world's oldest horse or not I don't know but a quick Google search finds claims from the 1800's in America of at least one horse living into its sixties...
Queanbeyan Age - Friday 20 August 1909
National Library of Australia