Old Man's War universe

Enlisting in the army on his seventy-fifth birthday, John Perry joins an interstellar war between Earth and alien enemies who would stake claims on the few existing inhabitable planets, unaware that the conflict involves much more than he understands.

Retired from his fighting days, John Perry is now village ombudsman for a human colony on distant Huckleberry. With his wife, former Special Forces warrior Jane Sagan, he farms several acres, adjudicates local disputes, and enjoys watching his adopted daughter grow up.
That is, until his and Jane's past reaches out to bring them back into the game—as leaders of a new human colony, to be peopled by settlers from all the major human worlds,

...

Lieutenant Harry Wilson counters hostile alien forces, angry humans, and unpredictable elements from the universe in order to protect the interests of the Colonial Union.

"Fans of John Scalzi's "Old Man" universe, prepare yourselves: there's a long new story in that universe, told from the point of view of one of the series' most intriguing characters." "Subterranean Press is proud to present The Sagan Diary, a long novelette that for the first time looks at the worlds of the Hugo-nominated Old Man's War and its sequel The Ghost Brigades from the point of view of Lieutenant Jane Sagan, who in a series of diary entries...