Manga where the main character is trained by martial master that he thinks is a wizard

Might this be Wizard's Martial World?

At the age of 78, Midran, an archmage is still searching for a way to reach 8th circle. Then he is suddenly turned into a child. Will he be able to recover mana from his past life and become the Archmage of the 9th circle? This is the story of the archmage's struggle in the Murim...

The story begins in a place resembling medieval Europe, and centres on an old wizard named Midran, who wonders if he'll ever manage to progress from the "seventh circle" to the "eighth circle", a level of mastery so rare among wizards that it is attained only once every few centuries. He goes to sleep in his bed, and a disembodied voice states that when he awakes, he'll be surprised to see that he is no longer alive, and his face will be a little different.

He wakes up as a boy named Hyun, in a place resembling ancient Korea; the boy's parents are understandably confused and concerned by the fact that he doesn't recognise them, or know where he is, or even speak their language. His memories are still those of the wizard, Midran, although he longer has his powers, and senses no "mana" in this place. Nonetheless, he settles into his new life, learns the local language, and resolves to rebuild his mana and recover his previous level of power, before finally ascending to the eighth circle.

A few years later, a military general, who happens to be a friend of Hyun's father, comes to visit. Hyun senses powerful mana within this man, and wonders how he could've gathered so much of it in a world where he detected very little. The general explains that this energy is ki energy, something he's learned to focus through his martial arts training. This piques Hyun's interest in the martial arts, and he begins to study some of the principles himself, not because he wishes to become a martial artist, but purely as a means of rebuilding his mana and becoming a wizard once more.

I believe this is Doryoku Shisugita Sekai Saikyou no Butouka ha, Mahou Sekai wo Yoyuu de Ikinuku, or The World's Strongest Fighter Who Tried Too Hard Living a life of leisure in a world of magic.

The first chapter is a boy being reincarnated into a world full of magic users. Once he is old enough, he asks his parents for a wand. They then knock him out and abandon him in a forest. He is found by an old man who was in the hero's party 50 years before hand. After training for years, an old enemy of the heroes appears. The boy defeats it in one punch. After that, the old man tells the boy that he was has no mana so he can't use magic.

Some more stuff happens after that, but in chapter 15 the boy goes to visit one of his teacher's team members. She gives him medicine to try to help him gain mana. It results in his body turning into a 3 year old after drinking too much of it.