You're not being penalized, you're being filtered.
You have to do something or provide something that is clearly different than those other sites. Maybe you are, but it needs to be obvious to your users and to Google.
If I were you I would forget about AdSense and don't worry about Google yet, but work on building your community first - you need users that love your site and come back to it over and over because they find something there they can't find anywhere else.
It means you may have to go GET your users, instead of waiting till they happen to find you in Google.
And make sure the percentage of content that is found other sites is relatively low compared to the amount of content that is unique. If 10 or 20% of the content is on other sites, you're probably okay. But if 90% of what you have can be found elsewhere, then you probably won't do well with Google.
That's just the way it works.