Also, you have to take into account which category rank youre looking at.
Figter, Attack, Bomber....
As has been mentioned, overall rank is a pretty unreliable measure of "how good youre doing", and it in no way reflects skill level. Rank can (and IS) be padded rather easily and with little fighting skills neccessary... you just got to know how

.
If you want to see how youre improving in single categories, take a look at the scores and watch things like kill/death ratio, hit%, damage vs objects etc.. to monitor your progress.
But always keep in mind outside factors! Ill give you an example: Last tour, my k/d was roughly above 1.0.... in itself a relatively low number. BUT, considering the fact that i was flying mostly Hurricane Mk1 in the late war arena (against much better performing planes) and that i have a habit of heading into the biggest red dar i can find with little concern to my altitude - im rather proud of such a high k/d.
Also, the single most important thing in this game isnt ranked or scored anyway: Having FUN! Dont get too single minded on achieving a good ranking, as long as youre having fun and achieving your own set goals (not comparing them to others) youre on the right track.
PS: To answer your question, usually each month there are around 4500 active accounts. Take a score where you do not have any figures yet (ie 0) and check the number in brackets... thats a rough estimate of lowest rank).