[PSY]

I'd say at LEAST two years before getting engaged (in my experience, there were a few key issues that didn't come up until after two years), and another year before getting married. During the engagement, I feel it's a good idea to move in together... get a feel for what it'd be like to live together, maintaining a house/apartment together, etc. I don't feel it's necessary to have sex prior to marriage, though (that's a personal choice on my end - I feel there are other ways to assess your "chemistry" without risking pregnancy).