Bounty Hound, it is a long way from new to antiquity.

As for which songs are old enough to be folk, I wouldn't know. But there are many songs that are old enough to be 'not new' which are still not folk songs and are not yet antique.

If a song was written yesterday it would not have had time to be distributed enough to be accepted as folk.

Unfortunately most songwriters are not widely enough known for their songs to enter the tradition; however good and folky their songs might be.