Old Man's War (Old Man's War, #1)

by John Scalzi

“But ultimately, you should care because you’re old enough to know that you should. That’s one of the reasons the CDF selects old people to become soldiers, you know—it’s not just because you’re all retired and a drag on the economy. It’s also because you’ve lived long enough to know that there’s more to life than your own life. Most of you have raised families and have children and grandchildren and understand the value of doing something beyond your own selfish goals. Even if you never become colonists yourselves, you still recognize that human colonies are good for the human race, and worth fighting for. It’s hard to drill that concept into the brain of a nineteen-year-old. But you know from experience. In this universe, experience counts.”

that one better reflects this book. fun read for sunny beach holidays.