Is 20 too young to get married?

In general, I believe so. Most 20 year olds have not experienced life enough, matured enough to take on the responsibilities and constraints of marriage and in most cases, at a bare minimum, will later regret not having experienced more before taking them on. Having said that, I have a niece who married at age 17 which we all thought was solely to escape a dysfunctional family situation and would fail miserably. But here it is, some 30+ years later, and she and her then also teenage beau have built a successful life together, raised their own family, and she is a grandmother. So it really depends upon the individual and circumstances.