I sincerely think the age differences is not a barrier.
Do you think the family of the girl will allow her to marry without her finishing her school?
Will you be responsible for her schooling if you did marry her?
Though the world is moving at a jet age.yet experience counts.can she handle a home and family at 18 years. Is she emotionaly stable to handle the inextricable rigour of wedding? If this questions are well tailored then you can go ahead.