I think the oldest UFO in my possesion is one I decided to finish that my mom started in 1947. By the time I was old enough to notice, my Mom was too busy to do handwork. I wish I had seen all the lovely linens she did while she was still with us.
The two quilts am proudest of took 14 and 15 years to complete. The old story of I can't look at this one more day, then drag it out later and work on them some more paid off. If I had just kept on working on them I wouldn't have liked the finished product.