I become US citizen ,can be use this like an opportunity for my son ?

Unfortunately, becoming a U. S. citizen will not benefit your son’s case as the current availability date for the F-2B category for unmarried sons or daughters over the age of 21 of a permanent resident is shorter than that for the F-1 category of unmarried sons or daughters over the age of 21 of a U. S. citizen. In the month of August 2016, the current availability date of the F-2B category for most countries of the world is 1/8/10 while the F-1 category is behind that 5/22/09. If you wish, your son can communicate with U.S.C.I.S. to preserve the F-2B category listing. Due to the limitations of the Lawyers.com Forums, Alan Lee, Esq.'s (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.