What are "old hymns"?

I used to play is what would probably be called a "folk group" at church. One day an old lady came up to us and said she liked listening to us play, but wished we would play more of the old hymns. I asked her which old hymns she particularly liked and we would see whether they could be arranged for the instruments we used. She mentioned two very old hymns, and two fairly new hymns our group had introduced several years earlier and had been taken up by the organ (which played at another service). So now because they had been played at the more "traditional" mass with the organ and sung enough times, they were now considered "old hymns".

Bagpuss