A friend of mine had an old embroidered quilt top with various spots that developed during storage. My quilt guru (she's been quilting for over 60 years and taught me) suggested soaking in tub with a bunch of denture tablets. That worked on those particular spots.

not AGE spots, but ACID spots...they do not always come out!

soak for a few days in oxyclean or efferdent!

I have seen good reports of RetroClean. http://www.retroclean.com