Injured Juvenile Collared Dove

Hello, I found a juvenile collared dove in my backyard a few days ago. It was just sat in front of my door and didn’t budge when I came out, it allowed me to pick it up without any resistance.

Upon seeing the dove walk I saw that it had a significant limp and I took it to the vet, who said that the leg is not broken but it is injured so needs time to heal.  They gave it me back  as they said they would put it down otherwise. I bought a large cage to house it in and have given it seed, water and some cut up carrots, lettuce and broccoli.  When it is walking normally again should I release it?  Or because of his/her age, will it not fare well in the wild and therefore should I keep it?  Any and all advice is welcome.

thanks

Nat