I imagine if you live near a large body of water, that it might be windy, in which case having a range of gears might be nice.

Are you OK with doing some of your own maintenance? If so, it expands your options. Within that price range it might be hard to find a new, name-brand bike. Your other options (big-box store, used, or mail-order) are all cases where being able to tune up a bike yourself will improve your experience.

I'm 55, and I find that comfort is pretty important, even when I'm out for exercise. Bikes are often shown with really low handlebars for a sporty look, but practically everybody I know who wasn't born on a bike, raises their bars.