Shinmai Ossan Boukensha, Saikyou Party ni Shinu hodo Kitaerarete Muteki ni Naru. S01

It's obvious to everyone that the earlier you become an adventurer, the better. Because the magical power that is the foundation of an adventurer's power, if not trained in youth, grows with difficulty. But Rick Gladiateur, the man who became an adventurer at the age of over thirty, had the fighting power of an S-rank adventurer, the highest rank in the world.