"Time runs differently in the mound." -The Moorchild, by Eloise McGraw
In an ancient Irish tale in the Fenian Cycle, Oisin traveled across the sea to Tir Na nOg (The Land of Eternal Youth). He lived there for a time then asked to go home to Ireland to see his father. His lover was loathe to let him go, yet she let him go bidding him stay on the horse. Once back in Ireland, he found that his father, Fin Mac Cool, and the Feanna were gone and it was years later. Then, in aiding some men move a boulder he fell off the horse onto the ground and was instantly transformed into an old man.
In The Moorchild, by Eloise McGraw, published in 1998, a similar circumstance is reported, or more like, she wisely drew upon the lore of yore. A fisherman named Fergus entered the Mound (the home of the Folk, as they are called in the book, basically mischievous little people in keeping with fairytales found in The Book of Fairies and Elves, by Olcott). When Fergil was later sent forth from the mound he transformed into an old man and found that years had elapsed, "five-and-fifty years older" (The Moorchild).