Dave,
The term 'old' which we found to be used regularly by source singers, is an odd one.
One of our best and most stylish singers, the blind Travelling woman, Mary Delaney had a large repertoire of traditional songs. These included several which had been made by Travellers themselves within say five or ten years of our recording them. They were usually about other Travellers - successful business transactions, selling livestock, playing tricks, personal experiences – in other words, everyday events of Travelling life. Many of these songs referred to people who were still living. She gave us one song and told us, "don't play that to anybody; it's about my cousin and he'll be furious if he hears it". All of these type of song Mary referred to as "old" and on every occasion she (and other singers) did not know who the authors were.
On the other hand, Mary also had a number of American country songs, some dating back to the 1930s and 40s which she described as "modern". Incidentally, She persistently refused to allow us to record her "modern" songs because she said that she only sang them because she had only learned them "to sing in the pub because that's what the lads asked her to sing". She insisted that if we wanted the "old" songs, that's what we were going to get!
As far as I can see the term 'old' refers to a type of song and its subject and function rather than its age.
I agree entirely with Snuffy, Greg and Ron; the tradition is a process and a song has to go through that process before it can wear the tee-shirt.
Jim Carroll