Like most aspects of people (age, hair color, height, weight, etc). it's of great importance to some, and of little importance to others. I would only offer a word of caution with this *particular* issue though. Some men, as they wander into the "Mid-Life Crisis Zone" go through phases of needing to reassure themselves of their manliness, studliness, and sense of adventure. This can be in the form of buying a sports car, taking up extreme sports (that aren't safe for guys half their age), or dumping their wife of 20 years for a 20-something trophy wife (who dumps them in a year). So be sure that the guy you may be thinking about is actually attracted to women much younger than himself (more importantly, attracted to YOU, versus your age). Otherwise you could be setting yourself up to be set aside when he decides a Lamborghini, or taking up base jumping, would express his youthful studliness more brazenly... not uplifting, but hopefully helpful. :-/
M