Activity for Mr&Mrs Smith

I've been anxious lately and have been wondering when is it ok to start looking and trying on dresses? I know right now is probably way too early since I am not getting married for another 2 years lol, but when is the right time?

My boyfriend and I are not officially engaged but we have been together for 4 years and have set a date. We both come from very strong christian backgrounds where it is a belief that its not a "sure thing" until he pops the question and a ring is on...