My mother is married to a USC and we are sending papers to file her I-751 right now because her GC expires on September. Mine, however, doesn't expire until April.

I know that my GC is dependent upon hers; I was wondering if this was also true in terms of citizenship.

Around this time next year, if the conditions on her GC are successfully removed, she would be eligible to apply for citizenship. If I were a minor, I think I read somewhere that I'd automatically be included with her application. There was just another form to be filled out. However, I will turning 18 this year.

How would this affect my status? Does this mean that I have to wait 5 years before I can apply for citizenship? Can I even apply for citizenship (considering I'm not the spouse of the USC). I wasn't adopted by my stepdad either.

If I can apply for citizenship, does that mean that I have to apply at the 3-year or 5-year mark of MY GC, and not my mom's?

I'm also moving away for college. Will I be filing with the state I'm living in or do I have to file with the center that my mom filed in?

Thank you for all the answers! This whole process is just so confusing.

Only a person who is married to USC can apply for citizenship after the 3 years marks on their GC. It doesn't matter if your mom is married to a USC, you mark period to applied for a citizenship is 5 years. Now that you will be 18, you won't get a citizenship either from your mom, but could apply on you own when you turned 5 years holding a green card.

If I'm wrong please correct me.

Okay here is more clear:

8.1)...When can I apply for United States citizenship?
A...As a spouse of a US Citizen, you can apply for citizenship 3 (three) years after approval of your Adjustment of Status. Back at the AOS interview, your passport was stamped with the I-551 stamp and a date. The 3 year countdown begins with that date. This 3 year period does not include long absences from the United States.
If you came to the United States on a K2 visa, you can apply for citizenship 5 (five) years after approval of Adjustment of Status, as only spouses of US Citizens are eligible to apply for Naturalization after 3 years. However, if a K2 is very young, it is possible that they may be naturalized along with the parent, if the parent becomes naturalized before the K2 turns 18.