Old Man’s War by John Scalzi is a good, fun read. It’s nicely in the category of hard SF in that it explores some classic SF concepts. We’ve got interstellar travel with a ‘skip’ drive, genetic enhancement, embedded computers and hostile aliens.
It is set about 200 years into the future. There have been some wars and mankind has spread out among the stars. A couple of interesting things seem to have happened. Earth is still there and doing well, but the nations of Earth seem not to be in charge of space at all. The colonies have taken over and limit access to space to two forms. If you are from an undeveloped nation with a burgeoning population, you can elect to be a colonist. This means a free ticket to some planet where you get to do ‘colonial’ activities. We don’t learn too much else about this branch of the space selection because the main storyline follows branch 2.
The second method of getting off Earth is open to members of more developed nations. Specifically, it is open to you upon your 75th birthday. You get to sign up to serve as a soldier for the Colonial Defense Forces (CDF). In some unspecified way, it is presumed (strongly implied) that you will also undergo rejuvenation of some sort so that you will be capable of being a soldier. When you join there is this paragraph:
I understand that by volunteering for the Colonial Defense Forces, I consent to whatsoever medical, surgical or therapeutic regimens or procedures are deemed necessary by the Colonial Defense Forces to enhance combat readiness.
The reason that soldiers are needed is that a number of alien species have been encountered and it seems that they are quite interested in the same general planets as humans. In general, they are also interested in killing (and sometimes eating) those humans to get at those other planets. Why the hostile aliens don’t show up until after we have found interstellar travel isn’t specified (there are three sequels, so maybe more info will be forthcoming).
The main character is one John Perry. We meet him as:
I did two things on my seventy-fifth birthday. I visited my wife’s grave. Then I joined the army.
That’s the first sentence, by the way, and it’s a pretty good first sentence as these things go. He and his wife had signed up for the CDF ten years prior to the opening of the book. A few years later, she had died of a stroke. John has nothing in particular keeping him on Earth and he isn’t particularly liking getting old, so it’s off to the stars for him
During the rest of the book, we follow John as he gets the “procedures deemed necessary”, undergoes training and then serves in the CDF. There’s some good action, but the book isn’t just about action and killing aliens. There is also a good amount of discussion between recruits as to what is going on–they do start out at 75 and so aren’t just fresh-eyed recruits.
I enjoyed this book. I’ve already started the sequel–The Ghost Brigades. There are a few places that are a bit info dumpish, but the info is interesting and in general, the writing was quite well done.