Old Man’s War
Scalzi’s debut novel is a stylish homage to Heinlein.
The central conceit of the novel is that the human Colonial forces recruit citizens of the wealthy western nations to become solidiers as they reach 75 years old with the lure that they’ll be young again and out defending humanity among the stars. It’s an idea that Scalzi has a lot of fun with as the new recruits go through basic training and on into relentless battle.
The prose can be a little lumpy at times and he’s not quite worked out how to show instead of tell, but it’s quite a lot of fun.
I’d recommend it if you’re looking for a diverting piece of old school science fiction