So, funny thing about teenagers. Their brains are still developing. In fact, the human brain doesn't finish developing until a person in their early-mid twenties. This includes things like impulse control, forward thinking, problem solving, decision making, being able to adequately determine whether a situation is safe/dangerous, and a lot of other extremely important things adults need to know how to do.
Teenagers (particularly those under the age of consent) have no business deciding who they'll be with for the rest of their lives. I thought I was going to marry the boyfriend I had when I was seventeen. Looked him up ten years later and, guess what? He's homeless with a felony conviction. Not great judgment on my part at seventeen. Really glad I didn't marry that dude.
Wanting to get married means very little when you're a teenager. You don't have the mental capacity to think through the long term consequences of getting married, much less whether you're with the right person.