I have absolutely not experience in this area, but I just wanted to chime in with support. I think that's a fantastic idea. I've heard that it can be done, and I would absolutely try it myself if I were in your shoes. As you said, I can imagine that nursing from the breast starting from such an advanced age could be difficult, but even if it is, he'll benefit from drinking breastmilk from a cup.
Congratulations on the adoption, and good luck!
Congratulations on the adoption, and good luck!