600 posts over 6 years and 8 months is less than 100 posts per year. So in three years you'll have under 900 posts. So at the rate you're going it will be at least 5 years before you hit premium.
Yea, but you've forgotten to take into account that, for like the first year or two I was on here, I posted outside the Spam Zone maybe a dozen times. I tend to disregard everything I did before about 2009, internet wise, so it's more like just over 100 posts in a year. So maybe more like three and a half years.
You'll need to bring this to me in graphical form, signed in triplicate before I can consider it valid for my findings.