David Foster and Katherine McPhee (34 Years)
With a quick glance at our next couple, one might assume that famed musician, composer, and producer, responsible for writing, and producing hits for the likes of Whitney Houston and Michael Bublé, as well as composing the scores for many hit movies, just picked up a much younger armpiece to show off at parties, but Katherine McPhee is a successful singer/songwriter in her own right. Despite their 34-year age difference, the couple boast of a very happy marriage where they often work together on a variety of music projects.