Age has so little to do with it for me except that many in their early/mid 20's have very few skills and often unresponsive in my experience. They have seemed more distant than present. 30's seem more skilled and more into it.
40's really know what to do and often more into it ie Lady Vanessa, April Showers. I have seen a few older and was surprised at the skill level being good.
All that said, I also have a few fwbs and one over 60 has the most amazing skills and can orgasm while 69ing over and over. She is still in good shape even though there is some sagging of skin but her pussy looks and acts like a young woman who wants it. She lately is the standard to compare sp's to even though some may not think that is a fair comparison but those are the cards I have been dealt. I also notice that when an older gal orgasms her afterglow smile makes her face look 20 years younger.
Just think, if one is blind the age of the sp would be tougher to determine and it would come down to the energy/connection and skill level.