If a 40 year old healthy man hasn't taken a flu shot in over ten years, should he start now?

Yes. A flu shot is not a series of shots; each year is a separate and different vaccine. The flu vaccine for a particular year is only designed to protect against the 2-4 strains determined to be harmful for that year. The next year would likely be different strains and thus a different vaccine. Vaccination is important to prevent your flu and to prevent you from spreading the flu to others.