I personally would never dream of being engaged to someone I hadn't been dating for at least more than a year. But maybe it's right for some people.
As for living together before marriage... well I am doing that right now, but we didn't start living together till after we got engaged. And we're only living together now because economically it makes sense, since we're getting married in less than a year anyway. It's impossible to live without a roommate unless you make a lot of money in this area, and it would make things difficult if we were both stuck in leases living with other roommates when we get married. The plus side is that we are finding that we live well together
I guess high school sweetheart marriages could last... I mean, there's no set time at which each person will meet the person they were meant to be with. I know that in my experience, my HS sweetheart and I don't even speak to each other anymore.