My father is a permanent resident and is married to a USA citizen. I was a minor less than 18 years old when they married.

You are her son or daughter for immigration petition purposes. She can petition for you. The INA defines “son” or “daughter” as someone who has at any time met the definition of a child in the INA Sec. 101(b)(1). You did, so she could petition for you and whoever is telling you otherwise is incorrect.

United States Citizens can petition for their "children" (unmarried and under 21), "unmarried sons and daughters" (over 21), and "married sons and daughters" (any age). It sounds like whoever told you that is confusing the "children" designation with the "unmarried sons and daughters" and "married sons and daughters" designations. You should be fine.

Hi, as the other attorneys explained, your stepmother can petition for you, but it will take long time. The current priority date (the date that an I-130 was filed) for an F1 immigrant visa (your category) from Dominican Republic is Oct 1, 2007. I assumed that you are unmarried and from the Dominican Republic.