John Scalzi's [b:Starship Troopers|17214|Starship Troopers|Robert A. Heinlein|http://d.gr-assets.com/books/1348024291s/17214.jpg|2534973]
(a book I haven't actually read for some reason, but the film is a guilty pleasure). John Perry is an old man of 75. His wife had died a few years earlier, but previously they had both signed up for the Colonial Defence Force – the CDF only takes American recruits once they reach the ripe old age of 75. Perry doesn't know why or how – nobody does. But signing up for 2–10 years means that the CDF must have some technology for extending life. Maybe that's why so many 75-year-olds sign up. Over 1,000 other people sign-up in the same group as Perry. But it's a jungle out there, during the first year, they are told, 40% of them will be killed.
Human colonists need defending, and the CDF is the muscle they need. Defending human colonies against aliens, and making pre-emptive attacks against alien colonies to allow more human colonies. I'm not quite sure how Earth is so insulated from what's going on outside. Apparently the CDF has little compunction attacking alien planets – why aren't they trying to return the favour?
Military science fiction has a tendency to end up falling into patterns of troop movements and military strategy over characters and relationships. Scalzi presents a number of characters, in the clique The Old Farts, who are centre of the story. Their training, friendships, and even losses. There's a slightly awkward set piece where Perry starts to fall apart after slaughtering a large number of small, defenceless, aliens. But, overall, Perry is a well-written, rounded and enjoyable character. A 75-year-old widower, coming to terms with his new lease of life, while trying to balance that with his new role as a soldier.
Also, especially for military sci-fi, there's a lot of humour. Both in the story and the characters. Not jokes as such, although Perry does seem to fancy himself as something of a undiscovered comedian, but the sort of humour that any group of people working together develop. Scalzi does like to throw in a couple of other surprises, especially with the character names – I spotted recruits with the names Gaiman, McKean and even Bender; I can't believe there weren't others that I missed though. Already added the next in the series – [b:The Ghost Brigades|8934762|The Ghost Brigades|John Scalzi|http://d.gr-assets.com/books/1316128034s/8934762.jpg|18279845]