Have a passport that is less than 6 months old

I am a US National residing in China with proper permits, etc. My US National son who resides in USA wants to come visit, but his passport is less than 6 months old. Will he be allowed to obtain ANY sort of visa? He will only be here 3 weeks on this visit, but because we will remain in China for the next 5 years, we would like to get him a multiple-entry one if possible. Any help is appreciated!