How young is too young to get married?

I am between the ages of 18 and 22 and i want to know. the man in quesion is my college sweetheart and well he can tick me off and make me smile at the sametime, also he fufills all i want in a man so i said yes. Anyway i just want to know if it was going to last, since i am not a risk taker. i am also going kinda of scared too. is that normal? we are going to have a poor man's wedding and have another when we can afford it. i just wanted to know