Hachi-nantte, Sore wa Nai Deshou!
I will rate this after I am done with other anime and stuff
One day the main character dozed off at his salaryman job and woke up in a new world as a five-year-old child. He was the 8th son of a very poor Knightdom. However, it also turns out he has an absurd amount of magic. After learning and mastering all the magic, his teacher could teach him. He finds himself trying to survive the day to day life of being a dragonslayer.