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

Synopsis:
“If you want to chase after your dream, then you better do it while you’re still young.” Everybody thinks that way. But sometimes, some adults will never give up. In a world where it’s common for someone to become an adventurer in their teen, Rick Gladiatol, a former guild receptionist who is 30 years old, aims to become an adventurer.
After going through unimaginable training by the members of the continent’s strongest party, the Orichalcum Fist, he tries to become an F-rank adventurer while having the capabilities of an S-rank adventurer.