Regarding A-2 visa dependents

Dear Sir/Madam.
My wife and I have a diplomatic A2 visa status while working with a foreign government in USA since 1977. On Oct 1983, my child was born in the US. Then we went back for good to home country since Mar 1985.

My question:
1) Is my child eligible to apply a US Passport in US Embassy of home country as a US Citizen since he was born in US and already have a long form birth certificate issued from the state he was born in the US?
2) Are there any others requirements in order my son can apply the US Passport?
3) Or Are there any regulations/law that my son is not eligible to get a US Passport if his parent while in US holding a diplomatic A2 visa status?
My son age now is 26 years old, still single and would like to continue his study in the US.

I appreciate much for your answer. Thanks.

Regards.
Redy
Redmac7@yahoo.com