Is it too soon for my boyfriend and I to get engaged?

I'm 20 and hes 21. we've know eachother for 8 years but have only started dating 5 months ago. We've been living together for 3 months now and have always talked about getting married and having kids and spending the rest of our lives together. We're planing on a 2 year engagement so its not like were rushing things. We know that this is what we want... I'm just wondering how others feel about such a short courtship before an engagement ... thanks for your help =)