Need to find this book


I believe I read this book close to ten years ago but it was in a paperback so it could be older. It was a fantasy novel and the main character was the youngest son of a hero/general/famous warrior. The MC had never met the father as he had died/disappeared when the MC was very young. He was raised and trained by his grandfather don't remember what happened to the mom. Another thing I remember was that certain skills, like fencing and chess, had ranks and they were given badges to represent their rank. The MC's grandfather refused to let him take the tests? to gain above a certain rank.
The only other thing I remember is the twist at the end, which was that the reason the MC had never met his father was because he actually was his father. Apparently he had gotten trapped in a magic storm? and was transformed back to the age of a baby. The MC's family made a deal with the enemy he was going to fight before he got transformed. They would raise the MC exactly the same and the enemy would let them live so that he could have the battle that he would have had originally. I'm pretty sure the enemy was a crazy wizard type as well.
Hopefully this jogs someones memory cause it's been driving me nuts.