Found young parakeet - advice?

Yesterday, we found a young parakeet, hobbling in the road. We took him in, worried that he would be run over by a car or attacked by a cat. He seems very sociable and used to people, not scared or nervous around us at all, and didn't seem bothered by the cage we put him in so we thought he might be a domesticated pet. But today he was in the cage in the garden and began to squawk. Suddenly, around 4-5 parakeets began circling our house, flying overhead. We opened the cage up to let him go but he was unable to fly, despite attempting to, so after a while we took him back in. 

Is there any advice you could give? He seems quite young - maybe four months, but in my understanding, they should be able to fly by now. We're not quite sure what's wrong/what we should do.