I had one that was foisted on me by a random stranger whose kids had picked it up off the ground. It was disabled from its fall, and would have been instant hawk food, so I kept it. It lived to be, hmm, 5 1/2 or 6. In the wild they normally live no more than 1 1/2 - 2 years. It was indeed a good pet if you decide to keep it.
My sparrow ate waxworms for preference. Most bait shops have them. Also mealworms and smallish earthworms, but the waxworms were his favorites. Think he started on the waxworms at about the age yours appears to be. Soft fruit, berries were also a hit, as were finely grated carrots. Green salad, not so much. I gradually switched him from baby food over to finch food just by offering a little dish full of baby food mixed with the adult food, then gradually increased the amount of finch food. I kept giving him some of the powdered, un-mixed baby food sprinkled on top of his seeds and bugs for several months IIRC, to be sure he was getting enough nutrition.
Also, your sparrow will want some calcium. They can in fact figure out how a cuttlebone works, or the oyster shell stuff you'd use for finches, parakeets, etc. will also work. And of course he'll need grit.
Good luck!