Old Man's War -- John Scalzi

In John Scalzi's future, you can join the Colonial Defense Forces when you're seventy-five and go out among the stars to fight for humanity's survival. Somehow the CDF will "improve" that old body and make it fight for fighting, but no one can find out how until he (or she) joins and is sent up the beanstalk. And that's about all I'll say about that. I don't want to spoil any of the book's surprises.

Old Man's War is narrated by John Perry, who joins the CDF after the death of his wife (they'd planned to join together). What happens next might be vaguely familiar to fans of Robert Heinlein, and Scalzi couldn't be happier if you find that to be the case. In some ways this is an unabashed tribute to Heinlein and Starship Troopers, but it's also reminiscent of Joe Haldeman's The Forever War, which I believe was Haldeman's response to Heinlien.

Another thing the book has going for it is good old-fashioned storytelling. A lot of contemporary SF leaves me cold because the writers seem to have forgotten that necessary element. But Scalzi hasn't. I mean that as a high compliment. And I like the writing style, too: simple, straighforward, supple, graceful.
I thoroughly enjoyed Old Man's War. Check it out.