If it is to judge the things from the grooms’ perspective then of course the whole wedding has to be about them and should reflect their preferences in everything. But don’t forget that without guests there is no wedding so in a measure you have to try to please everyone.
So like when choosing the wedding music you think about wheat you like most then about your guests and what they like for mature couples, old ones you choose old songs, contemporary for youngsters and so on.
At your task of making the music selection for the wedding don’t forget about the key moments. Include the grooms’ first dance, then the dance of the bride with its father and of the groom with its mother. But aren’t grandparents included as well? Godparents as well? Not that there is a tradition or imposed thing about this but they all wait your attention; it is your respect towards them. But as how godparents may be appropriate as age with you or with your parents and easier it will be to select a song for their moment, your job now will to find songs that granddaughter and grandfather can dance to at a wedding. Or, depending on the case for the grandson with grandmother.
If it is to take their age as main reference as to determine what genre they would like then the songs that granddaughter and grandfather can dance to at a wedding should be of course old ones, excluded contemporary. Some titles may be “Say you, say me” by Lionel Richie, “Lost in your eyes” by Debbie Gibson, “All out of love” by Air Supply, “The best that you can do” by Christopher Cross, “Faithfully” by Journey, “Nothing gonna change my love for you” by Glenn Medeiros. And the beauty of ’80s can continue with George Benson or Cher, Peter Cetera, Chicago etc.11