Maryland law would control since the "marriage" occured there. As long as she was over 16 and had her parent's consent the marriage can not be annulled on the basis of her age. But you get an annullment if your consent to the marriage was based on the fraud by her that she was 18, but if you married her for other reasons that were not fraudulent you may not get the annullment granted. Visit the site below to see the law in Maryland.
http://www.peoples-law.org/family/divorce/Unlawful%20Marriages-WLC-1.htm
Annulment is a relatively rare special action that establishes that your marriage never existed. If a court finds the facts necessary to grant an annulment it is as if you and your spouse were never married. The factors necessary to prove an annulment are difficult to meet and therefore courts are reluctant to grant an annulment and may grant a divorce instead.
In florida if you had sex after the marriage you can not get an annullment even for fraud. see this site http://www.ablelegalforms.com/annulment.html - so it is good that Maryland law controls.
Lawyer (JD)
Attorney-Business degree from The University of Texas