As someone who's relationship moved fast at a young age, I'll let you know a few things. I'm 20, so maybe I can help you relate with someone your age.
I have KNOWN my husband for 15 months. Right after we met, he moved in. Not intentionally, more of he would drive me to work when I worked at 5am on days when the roads were bad because he had an SUV with 4 wheel drive. Well, we met in December, so it happened so regularly that he just quit going home. He lived with his parents, and one day his mom said, you know, you basically moved out. We were engaged a month and a half after we started dating, and were renting a house together over the summer. We got married this past Halloween. Even before we were married, we started experiencing a lot of HARD life changes. We both lost our jobs, were out of work for month, lost the house we were renting, both were extremely ill all summer, husband has thousands dollars in hospital bills.
Unlike most couples, I'm going to have to say so far the worst part of our relationship was after we came back from our honeymoon for maybe the first month. We were frustrated, had a LOT of things to deal with, and neither of us had a job. We couldn't figure out how to get bills paid, and each of us weren't willing to give certain things up. It took us a little bit of time, but we finally have everything figured out, and are happier than ever. Sure, we both work at Wendys fast food restaurant, and live in my parents basement, and share a vehicle, but have each other, and were able to keep the things most important to us, and we were able to sit down and make a 5 year plan.
I love my husband dearly, and if I could do it again differently I wouldn't, but it's not for everyone, and just because your engaged dosent mean you have to get married right away, some people wait 5+ years.
Whatever life brings you, good luck.