I haven't finished any of the game projects I have started, and I have been dabbling with game programming for over a year now.
I started off using Java 2D, then C++ with Dark GDK, and now XNA.
I think it's okay to not complete projects as long as you are increasing your potential.
The first computer game I made was on my ZXSpectrum. I wasn't very old, only about 8 years old, but it was only a simple game. A few years ago I found that tape and I converted it to a .tap file for use with an emulator. There was a few other little programs on there which I'd written. All very funny to look back on.
I became interested in making games about 6 years ago. I've finished about 8 games so far, having attempted about 20.
As for motivation, what I benefit from most is a time limit/ deadline. With personal projects I don't have one of those (self imposed time limits are meaningless), and I'll remain in first gear, maybe slipping into neutral.
But when I have a deadline, such as in a competition, I feel the pressure of time, which I like, and it pushes me up through the gearbox, and I experience flow
, which can be very satisfying.