The thing about age that I have learned is that I am usually wrong
I have found that the 20 somethings that swing tend to be more mature and the 50+ tend to be very aware of their appearance so I quit trying to guess as I have been pleasantly surprised more than once. I now focus on whether or not we are having fun with the couple and find an attraction. If that all comes together then who cares how old they are (legal of course).
One of my favorite partners is the same age as my dad but I didn't know this until many months later. They have become good friends as well as playmates.
The thing we have learned from our younger playmates is that they have trouble finding couples that will consider them because of their age. Like us, many assume that "the cute young couple" wouldn't be interested in us so they don't even speak with them. Wrong again.