If it's white and also on the cheeks - I would still suspect thrush - same treatment. When an older person gets thrush, it's usually because there is some type of compromise with the immune system - such as mono.

If it's just on the tongue, depending on the diet and lifestyle, it could be a very acidic condition in the body - especially, if there is bad breath to go with it. If the breath smells metallic, it could be a build-up of inorganic minerals. In this case, I would consider doing some type of cleanse to help bring the body back into balance.