It's not just a question of wingspan. Most birds have (sort of) hollow bones, which helps to keep weight down. And that's really important.
Additionally, actually getting into the air requires speed, and powerful muscles to flap the wings to achieve lift.
Another consideration is the weight of the wings themselves, and the strain placed upon the spine by them. Bigger means more weight, and more weight means more strain. If big enough, the kid could be a cripple by 20.
In order for your character to be able to get into the air and fly, it would need:
1. Powerful legs to build speed for lift.
2. To rely on wind,or high drop offs to build enough speed for lift.
3. Powerful chest and shoulders to flap for extended periods to brute force it into the air.
4. 160
Any combination of the above.
Muscles are dense, no matter where on the body they are, and that adds weight. In order to protect the spine, said child would need to have well developed chest, shoulder and back muscles, and be extremely lean. Bones would have to be, as previously mentioned, hollow-ish(think of a honey-comb structure), which makes them less resistant to breakages, and has a lower hard limit on how much weight they can sustain before breaking.
Nature imposes these limits on us all the time. We are the size we are, because anything bigger tends not to survive (giants have heart attacks, and skeletal problems due to weight).
So let's assume a wingspan of 10 feet on the child. By the time that child is 20, that wingspan will need to increase, and as such will also increase in weight.
Eventually, the muscle mass required to even move the wings would put enormous strain on the heart and skeleton(because humanoids have a leverage based skeletal/muscle structure), so flapping to generate lift would necessarily give way to soaring and taking advantage of thermal updrafts later in life. There is a reason that large birds tend to live in aeries: So they can jump out and build up enough speed to glide and soar. It's actually very difficult(and energy intensive) for them to get off the ground without strong wind. This means your flying child would have to have incredibly powerful legs, so that he could either jump VERY high in the air, or run REALLY fast to generate enough speed for the wings to generate lift efficiently.
The reality of your character is that even at 11 years old, he would look like a miniature body builder, and would be an athlete rivaling Olympic medal winners. And even whilst folded, those wings would reach well above his head, and would drag along the ground when he walked. 160