"That kind of reckoning would make "Alexander's Ragtime Band" a folk classic!"
It would if "old" had anything to do with a song being 'folk' - it hasn't so it isn't.
Several of the newly made songs we were recording from Irish Travellers were less than ten years old yet fell well within the description of being 'folk songs'. The same with the 'local' songs that were to be found all over rural Ireland, many of which must have been made during the lifetimes of the singers.   
'Folk' is a process the song, tune or story passes through' irrespective of how long it takes - days, weeks, years or centuries.
Jim Carroll.