It varies, when I hit 5th prestige I was already of quite a high ability in extinction.
There are different areas of play such as prioritising aliens, knowing when to and when not to do specific things and strategically placing yourself on the map.
Things like this are what make a good extinction player, people such as Stinky666 I consider an advanced players because he as good knowledge of these things.
I'm prestige 16 or 17 now and I feel I know enough to be an highly effective player.
Even back when I was 5th prestige people took 1 look at my stats and saw how valuable I'd be to have as a teammate.
I think that the biggest difference is "who" you play with.
Playing with the right team, you can learn the game very quickly.
Then your skill will vary on what skills you already had before trying this game. If you're already a good MM player then you only need to learn the mechanics of this game which is not that difficult.
The challenge in Extinction is not the game; the challenge are the players that you play with.
I remember that at first i thought that this game was impossible until one magical game where everything was so easy and I realized that I was playing with the "right' team; from that point i knew that I needed to be selective of who I play with.
You sound like me; I picked up this game very quickly. First, I watched some videos, got a general sense. Then I played a little solo, got a general feel.
I got lucky, I was put into a lobby with people who have prestiged (at that time, if you had a prestige, you were considered good lol). They taught me literally everything (some of it is wrong today, but it was the best information at the time). I considered myself acceptable (not able to carry a team, but able to contribute and not hold a team back) after my first prestige.
Nightfall was when I grew the most as an extinction player - I was picked up by a team of 3 one night and I stuck with them for 12 nightfall escapes (and 12 platinum escapes). Even to today, I learn things from other players all the time (currently on 15th prestige). It's all about having an open mind and constantly trying to improve yourself. A lot of people just play this for laughs and don't care about a thing (that's totally fine) but they suck as teammates.
So yes, it is all about the people you play with, if you had a great mentor or not, etc.
To be honest, I think I was a slow learner. I started with no mic and only seemed to play with low level players. I would usually get my share of kills but could never really carry a team and usually got carried if anything. I finally bought a mic (well- bought my kid a new mic and stole his old one) and found this forum. Too cool that you can access some of the best players in the world and ask your dumb questions. I'm now somewhere around 27 days played, max prestige, and I still feel like I learn something almost every day, sometimes just little things, where to stand, where to run, where exactly to point my sentry or set my IMS, but always try to keep learning. This is what keeps me coming back...every day. I never trash talk in a lobby and usually down play my ability in the lobby then let my stats at the end of the game do the talking.