I turn 30 in 5 months and can completely identify with how you've felt. I too have the dozens of domain names for long-abandoned web applications for some idea that I thought was a radical spike of insight at the time.

It's a vicious cycle. I get the idea. I register the domain name, already imagining a brilliant fully-featured yet astonishingly-easy-to-use product. I start cranking out code. But it takes some time. I realized some problems I thought were easy are harder. That takes more time. I realize a certain problem is exceptionally hard and will take me longer than I thought, so I hack together something that works for now. I realize yet another problem will take me longer than I thought, and a few weeks pass and I begin to feel my web application is just a series of hacks. If we're using the art analogy, rather than the beautiful and crisp design I envisioned, my canvas is filled with ugly smears and smudges that doesn't look anything like what's in my mind.

And it's always a lot easier to just throw out the canvas and start something new, than to tediously work out improving those smears and smudges.

So, perhaps one hopeful anecdote I can share: earlier this year I did start a project that I've finally been able to focus on. The only difference with this one vs. the others is that I saw a tangible return relatively early on. Two months after I worked on it, I made $72. That's basically a laughable number, except it's the first tangible return on the dozens of web applications I've started and abandoned for the past 5 years. From then on, there's been a mostly-positive correlation between "hours put into project" and "dollars earned," which has completely shifted my mentality.

I've begun to take pride in those smears and smudges, knowing I'm already succeeding to some degree and it could be especially rewarding if I continue. I have no idea if this would work for you, or anyone else, but like others have said, this is a process. Everyone designs and creates at their own pace, and age seemed pretty meaningless to me. In fact it's now that I'm older, instead of 5 years ago, that I can begin to appreciate my limitations and have the patience to work with them, instead of ignoring the fact that they exist.

And above all, be proud that in a world where many are content to maintain and manage (literally and figuratively), you have the desire and the ability to create and produce. Best of luck.