Niacin, niacin, and niacin. They grow fast and need lots of it in that time. Get some niacin tablets at
Walmart and mix 100mg per 1 gallon into their drinking water. Best is to get a bird supplement. I give that water for drinking for the first 10 days, then weekly and then monthly once they are 3 month old. It is really important for strong bones etc. Here is the product I like to use:
https://www.gqfmfg.com/store/comersus_viewItem.asp?idProduct=231 It's a powder and stores well.
Wrapping for angel wing is not that hard, but takes a little bit of practice. You learn really fast how it works right. The 4 month old one may be to old, but I would try it anyway. It is best when the wings lay tight to the body to prevent injuries down the road. You need to go to the feed store and get vet wrap (horse isle). Vets also carry it. It is a stretchable wrap that sticks to itself but nothing else. It comes in various colors. Avoid flashy colors, since it can scare the other birds. I usually use dark green or purple. Here is a pic of a wrapped bird.
The wrapping cost about 2 dollars per roll and one roll is good for two wrapping. Get 3 or 4 rolls. That stuff is good for lots of things so it is good to have. It can be used on humans.
Wrapping is a two person job. One needs to hold while the other one wraps. Place the bird onto a table so the feed have a flat surface to be on. The duck only need to be wrapped for half the day for 3-4 days. Take the bandage off at night so blood circulates freely, plus they usually rest anyway and don't move to much around at night.
Here are the instructions and I'm sorry I don't have images. Fold the wing under and wrap the wing once with the vet wrap. That will keep the wing in a sling and the bird cannot stretch it out. Next wrap around the body close to the feet, and one more time higher up over the chest. This should prevent the bird from pulling the wing up and out of the wrapping. Now you don't want this to be too tight or the birds cannot breath. Too loose and it will pull its wings out. They are Houdinis after all.
You will learn it as you go, and their will be some failure in wrapping. Everyone who does it becomes a pro after wrapping twice. Really.