A story about a powerful magician that reached his max. He was reincarnated into the future as the third son of a nobleman. His father taught him how to use a sword and was a great swordsman, but he beat his father on his first try. The second son was the heir because the first son was weaker. The mc then took the first son under his wing and taught him how to be more powerful. I think that's it. Oh.. the type of magic you can use is determined by the mark on your hand.

Shikkaku Mon no Saikyou Kenja