Old Man’s War does quite a bit for a single, short book. Not a lot of material here is necessarily new and that is fine. Sci-fi is a tried and tested genre and most readers should not expect anything too radical. We all go into books like Old Man’s War expecting to see spaceships with some kind of faster-than-light travel, laser/energy guns, etc. As far as military sci-fi goes there are two main types; stories about either the Space Army or Space Navy. Old Man’s War falls into the former, focusing on boots-on-the-ground soldiers.
It is hard not to compare a story like this to similar books, and Old Man’s War is more reminiscent of Starship Troopers than anything else. The military aspect is largely the same. New troops spend a lot of time training, feeling like badasses, to go fight aliens. But once the fighting starts, they are fully exposed to the horrors of war with staggering casualty rates. Unlike Starship Troopers, mankind does not mainly fight a single species of alien. The galaxy is basically a free-for-all with hundreds of different aliens involved. Everyone fights everyone; no species are truly allies. At best, there are some temporary “not enemies”.
There are a few other staples of sci-fi in Old Man’s War as well. Most species are roughly on the same technological level. The sole exception being the “one-above-all” species who could wipe out everyone else if they really felt like it. Like in most Army-type military sci-fi stories, the spaceships do not really do much. On the rare occasions they engage in combat, ships seem to turn into burning wrecks after taking a few hits. It is mentioned that ships have shields, but they do not seem to offer much in terms of combat protection.
For all the tropes, there are a few different things the book does extremely well. Case in point, habitable planets are rare. To the point where hundreds of alien races are in a constant state of war over them. Unlike most other series where every second or third star system can support life. Granted, Old Man’s War gives the sense that on a galactic scale, ships cannot travel that far. So, the limited distance does somewhat explain the scarce real estate. And, of course, the base premise of 75-year old people becoming soldiers. That was definitely a new one with the way it put older, more experienced people in boots normally reserved for young soldiers made for very interesting characterization.