Can you weigh him (perhaps on a kitchen digital scale) and tell us how many grams he weighs?
Also, feel the breast bone (the keel) to see if it feels prominent. If he has been eating enough on his own, or if he was being fed by his parents, he will have sufficient musculature for the keel not to feel too prominent, even though he may not be flying much yet.
From the weighing of the pigeons in Cologne I rehabbed, a healthy adult would weigh 330-350 grams. One fat one weighed 400 grams. He was a bit slow-flying, got run over by a car from behind. A sick adult pigeon would be in danger at less than 240 grams. (283 grams = 10 ounces). Females weigh less than males, but I am not sure of the ratio.
If he didn't have a deep dish to eat seeds from, he would have to lay his head sideways to the ground to pick up seeds from the ground, and I do not know if he would know enough to do this on his own, since he is so young.
I had a pigeon ("Splitbeak") with a split upper beak who occasionally picked up seeds with a sideways head position. But most of the time she would try to pick something up in a normal pecking fashion, and would drop the seed or bread crumb. If it were a large crumb, she might get it down. But usually she would make several stabs at the seed or crumb, fail, and another pigeon would get the food. Eventually she suffered badly from malnutrition, got diarrhea, and built up a golfball-sized rock-hard mass of poop near her vent (anus), which adhered to the feathers of her lower abdomen and feathers around the vent. I had to catch her, take her into the shower for a half hour to remove the crud, and keep her for a week to feed her up. Couldn't keep her, and had no alternative rehab possibility at the time. Rendezvoused with her everyday to sneak her a deep dish of seeds, out of sight or notice of humans, since feeding pigeons was a no-no, and out of sight or notice of other pigeons, who would draw attention to the pair of us. She would see me coming from half a block away getting off the streetcar and meet me at one of our semi-hidden spots. Eventually several other pigeons started to associate my appearance with food.
I monitored my rehabs by weighing them every morning before their first feeding to be sure they were maintaining a steady weight. Also, i watched their poops closely.
Gotta go. Best of luck, and thanks for caring for this young one.
Larry