When you look at your efforts as a writer from a financial standpoint (And you should, as an indie author), you can very easily get both excited and depressed. The fact of the matter is that even out of the 1-2% of the people who -want- to write that actually end up publishing something, a very small number turn into bestsellers. That is one part of the depressing news about being an indie author, or any kind of author, really.
The next bit of depressing news is that, for 99,9% of us, making a living off of being an indie writer is work. It's a job. You don't just sit down and make 100k a year from releasing your first novel. That's just not how it works. Unless you're extremely lucky.
The good/exciting news are that regardless of the above, it is very possible to make a living as an indie writer. If you have written, finished and published something, you are already on track. Now you have to stay on track. You have to have work ethic. Being a writer is not about a dreamy life in Paris cafés or seedy bars. All that comes after you've written.
No, the good news is that you can make it happen. You, and no one else. As long as you have a work ethic and keep writing and releasing, you are moving closer to your goal, if that goal is to be able to make a living off writing.
Let's, for the sake of argument, say that you release 2 works a month. Could be short stories, novellas, even novels. You price them at 2,99$, and you sell 5 copies of each. 10 copies a month. You earn roughly 2$ royalties per copy, so in other words, you earned 20$ the first month. Not impressive, but consider that those shorts stay on the market and sell, on average, 5 copies each per month.
Next month, you release another 2 shorts. Now you earn 40$ a month. In other words, once the first year has passed, you will have 24 works out there and be earning 480$ a month. Remember, this assumes no irregularities. You can certainly sell more than 5 copies a month of a given work, especially as you become easier to discover and perhaps even build up a fanbase. You improve as a writer, and you could end up selling far more. This is a -baseline-.
At the end of the second year, again assuming no irregularities, releasing 2 works a month, you'll be up at 960$ a month. Again, perhaps not impressive, but you're starting to get up there. Year 3: 1440$/month. Year 5: 2400$. By the time you're here, you're earning 28,8k$ a year. Not glorious, but certainly something to live on.
Remember, what you've written is for life, assuming you keep moving with the times and take advantage of new platforms, perhaps branch out into audio or the like. While income will slowly drop off over time, your books never stop existing. You are building up a solid livelihood here, income you can take with you into your senior years as well.
So, writing can be something that starts slowly, but remember: With work and dedication, it's possible to write for a living. Oh, and... Year 20: 115200$ a year. Again, assuming no swings back or forth. If you've been writing for 20 years, I would be extremely surprised if you had not managed to build up some sort of name for yourself. Consider the impact that could have. The number above still assumes you make 10$ a month for each story out there. It doesn't take into account any possible big sellers you might have, or popular works that never have a breakout, but consistently sell 25 copies a month, or anything else.
And here's the "best" part. You can do this even if you're not a prolific writer. Assume your average work is 5000 words. 2 of those a month means you can write as little as 330 words a day. For me, that's about 15-20 minutes of writing. So, if you're thinking about getting into writing but have children, a job, whatever, ask yourself: Can I set aside 20 minutes a day for this? If you really want to write, you'll find those minutes somewhere.
For those wanting a far more in-depth view of this topic, have a look at Dean Wesley Smith's blog post on the topic.