My commute is 11 miles each way, moderately hilly, very few lights. It takes me 45 minutes in, 35 back (a little more uphill on the way in). I would try doing "every other day" commuting for two weeks or so. I found, even starting from a pretty non-in-shape base, that I made rapid improvement with consistent riding. 16 miles is long enough (and you're a bit older than me as well) that I think it will take longer to get used to it.