>You've registered in September 2014.
>We're now in December 2017.
>That's a difference of 3 years and 3 months.
>That's 365*3+30*3 = 1095+90 = 1185 activity.
Of course, that's not the exact potential activity of your account, as I rounded it off to whole months and activity is only counted per 14-day period, but it's accurate enough to say that your potential rank is Legendary.
Anyways, can you please try thinking a bit next time? It's not that hard.
The BitcoinTalk Price Estimator tool showed your potential activity. But the website is now down for an indefinite period of time. So, you probably must calculate everything manually by checking your post history.