Quite often dentists will want to fill a 'hole' it's happened to me. When I was 10 my dentist wanted to wait & see what happened, that tooth has never been filled in the following 39 years, on 3 occasions I was told the tooth needed immediate attention.........

In any case once a tooth has been filled it won't last as long as a healhy tooth, obviousely you can get all your teeth filled if thats what you want!