will I still get my immigration under F2A while I am becoming 21 after 6 months?

From past visa movement, I do not foresee that visa chart movement will be over one year within the next 6 months. Your ability to immigrate under the F-2A category will likely depend upon the period of time that the I-130 petition pended or is pending before approval. The Child Status Protection Act (CSPA) gives a credit to your age for the period of time that a petition pends with U.S.C.I.S.. For example, if your father filed your F-2A petition in November 2011 and the petition was not approved by U.S.C.I.S. until November 2012, you would have an additional year plus your present 6 months in which you would be counted as a child under the age of 21. The I-130 approval sheet will show the priority date and the date of approval. 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.

You merely had to have an approved petition before you turned 21.  Since the petition is approved, assuming you remain qualified for the F2A category, you can process your visa once a number is available, which looks like early in 2014.