[Gymngatagaica]

اَلسَّلَامُ عَلَيْكُمْ وَرَحْمَةُ اللهِ وَبَرَكَا تُهُ

As far as I know, a girl can get married at any age so long as she has the permission of her legal guardian. Marriage without the consent of her guardian will be considered if she has past puberty, yet she should not do this.

If she is married without consent before puberty, then as soon as she hits puberty she has the choice to continue with the marriage or annul the marriage, and if she is married without consent after puberty, the marriage is not considered.

All of the above is what I think is correct according to the Hanafi madh-hab, but please do not take my word for it alone. Wait for confirmation from an 'Aalim.