Some times old is too old to use. It is great to RRR. As you learn more about material you will be more able to discern quality in fabric. It is a learning experience.
Another subject with a wide range of opinion is the use of sheets in quilts for the backing. Be careful with this sometimes they work and sometimes not.
The main reason being that the thread count in sheets is much higher than in standard quilting cottons and it can make quilting harder. If you machine quilt sheeting material the needle can tear the sheet threads rather than pushing through the threads. It can also cause distortion on the quilt top.
It is a choice and many will say they never have a problem using sheets. This is just a heads up on what can happen.
Don't get discouraged over the fabric you thought was a wonderful find. This one time the fabric was very thin.
A long time ago someone told me that if I could see my hand shadow behind the material it was too thin to use. I have used this test many times and I think my quilts are better for doing it.
Passing up beautiful fabric is hard to do sometimes but in the long run there will be other beautiful fabric in the future.
peace