Their are a lot of people making money online with Google Adsense. Great success stories, but it didn't happen over night. Making an earning will vary depending on many factors.
You have to understand the process of Internet marketing. In order to make money online you will become an Internet Marketer.
It also depends on how much traffic your site will receive.
Also how much you will earn per click.
And last, how many hours you put into your site daily.
People get caught up on how much people make that they start using someone else's success stories and use topics that makes the most money. It doesn't matter if a certain site makes over $2,000/month in Google ads, It matters that you go out and start your own topic and your own ideas.
The webmaster that created the site with a lot of traffic and making $2,000/month with Google Ads. Didn't do it over night, he created a site they he knows, that had a lot of useful information on his subject and overtime other people came to his site linking to his site and also blogging about his site. Eventually the traffic grew and his Google Revenue grew into what it is today.
Bottomline, you have to be motivated and know your topic that you enjoy talking and sharing about. All people learn at different speeds and the amount of time you put in the better outcome you will have at the end.
It will take time in building your site, you will spend many hours in front of your computer. Wondering am I wasting my time with this. Like I said before treat your site like a business. You will have a lot of trial and error but eventually it will pay off at the end.