Getting married at 20

Im 20 years old and I'm getting married in a couple months. Its nothing too fancy just a simple courthouse wedding. I've been with my boyfriend for 4 years, we're both in University and have jobs and we feel ready to take the next step. We're both really happy about it but it just annoys me that whenever i tell people their first question is "Why?!" And then their second question is "Wait, how old are you?" And finally they proceed to tell me ALL about how marriage is horrible and im making a mistake. I rarely ever hear a congratulations.