John Scalzi’s debut scifi adventure is amazing.
It tells a story of old people from Earth that are recruited for a intergalactic military organization. There, their bodies are reconstructed to it’s younger form and enhanced.
From there, they have to fight against alien races in order to protect humanity. Humans on Earth do not have a clue about this galactic war BTW.
I must recommend the reading.
Note: I also read the sequel, The Ghost Brigate. And also love it. But much of the original wow was, of course, gone.