How long will the waiting process be?

I just turned 21 and my parents' permanent residence just came in. I am unmarried and it says that in the preference list of petitions I am Second preference (2B) in the catergory to get my legal residence. I am already in the United States so i don't know if that will affect the timeline for this. can someone please let me know how long it would take to get my green card. I did not cross the border, I came here legally but overstayed my visa.