How long get the petition approval

Hi, Please allow me to ask you about my case I130 for brother /sister. that was received and filed by USCIS on 22 Aug 2012 . I’m would appreciated if you could kindly estimate how long I will get an approval of Petitioner.

Thank you in advance for your kind assistance in this matter.

Look forward to receiving from you.

Best regards,

Noi

My case is on 27 Sept. 2012 and I am still waiting !