I'm not really going to answer your question. But I am going to give you some insight into it.
My mother married my father when she was 19 and he was 17. They both claimed they were very much in love and would be together for the rest of their lives. They have been divorced for more than 10 years.
On the other hand, my grandparents married when they were 16 and 21. And they are still together as strong as they ever were.
Love is very fragile. It takes a lot more than just strong emotions to sustain it, it takes caring, understanding, compromise and trust. Not to mention a lot of sacrifice.
If you are both willing to make these changes, and trust me when I say this-things will change once you say 'I do', then you aren't too young.
You will both have to prepare for the changes that will happen during the next few years, not just with each other, but with yourselves. You will become different. Not saying that you will do a 180, but you will become more firm in some beliefs and lax in others.
All I can tell you is this, be prepared to make changes, don't fight with each other- talk. Communication is the most important part of a marriage. Never be afraid to laugh and always take everything with a grain of salt, even life changing events. Love unconditionally and never try to hurt each other or accuse each other without facts.
Last but not least, congratulations on your marriage, God bless you both and I hope you have a great life together. You can be mature enough at 18 to get married, I know plenty of people that aren't mature enough at 40. Good luck!
BTW, for the people that are saying that people over 20 will tell you that 18 is too young, I am 23. And I don't appreciate people speaking for me.