At the age of 70, I just baked my first sponge. It went well. But I found the icing/frosting recipe i used over-sweet.

Thank you so much!!

Here's a fantastic buttercream recipe. Adding egg yolks does wonders:
http://www.food52.com/recipes/3048_buttercream_icing

Otherwise, I would use a meringue buttercream or add some cream cheese to your recipe. If you are using a standard buttercream recipe (icing sugar, butter, and a touch of milk or cream), they tend to be overly sweet.