Here's an even older thread. As to the song's age:

[1965:] [The Galbally Farmer] One of the best-known humorous ballads in the South. [...] My father, John O Lochlainn, knew most of it from his childhood in Listrolin near Mullinavat, Co. Kilkenny, but he always sang 'The Gaabally Farmer'. (O Lochlainn II, 214)

This means it was around by the middle of the 19th century, I suppose.