回复：回复：回复：Is there anyone know about the age limitation

If you want to adopt your nephew with the intension to bring him to the US, then you must do it before he turns 16 to meet the immigration requirment. ( See lawyer Xu’s article)
You should contact the Chinese Embassy/Consulate to ask them for a copy of the Adoption Act. I read the Act before from the magazine, but I could not found it. As I remembered, there are some conditions for adopting a child in China. Good luck.