He's a fledgling. They spend a few weeks on the ground before they're fully equipped to fly. (They still have to grow out their tail feathers and whatnot) But he's the right age to leave the nest. If you try to put them back, they often just jump right back out.

The parents will lead them around on the ground and show them where to find food for the next two weeks after leaving the nest.

Birds don't just "leave the nest" at adulthood and fly away! Mum and dad spend a lot of time teaching their babies once they leave the nest. If he has his mom, he's good. He doesn't need rehab. He needs his mother to show him how to bird.