The 8th Son? Are You Kidding Me?.

Ichinomiya Shingo, an everyday twenty-five-year-old office worker, wakes up as Wendelin, the 8th son of an impoverished noble family out in the sticks. He soon despairs at his lack of succession rights and knowledge to navigate the political world, but finds hope in his aptitude for magic. This is the story of that young man earning his keep and his freedom through magic, with no world saving involved, and spending quite a while escaping his solitude. Ultimately, it is also the story of him being unable to escape the shackles of society.