Penitent

Michael didn't want to die. He didn't deserve to die. After a lost battle with cancer that started only a year after he retired, he'd lived what many people would call a full life, but it wasn't enough. He wanted more time. Time with his wife. Time with his kids. Time with his grandkids. When he found himself drawn toward the light, he fought his way away from it. Unfortunately, that didn't take him back to the life he wanted to live.

Reincarnated in another world, Michael is forced to be a Penitent, a soldier in the country he was reborn into in order to pay a debt to society he owes for taking the life of the child whose body he inhabits. It's not the life he wants, but it's the only one he has.

An Isekai with light litrpg elements

MC will gain powers similar to those of a paladin

Book 1 spends a lot of time in a military academy. MC does not stay a child for very long.

Story will be a slower pace than my others.

MC may not be to everyone's taste. He feels guilt for his actions that may seem unreasonable and is very human. He will grow, but it will take time.