I have recently become interested in the possibility of actually attempting to contribute to one of the many open-source projects out there. I'm interested in not only gaining development experience, but also gaining experience tweaking UI's, improving usability, etc. I found this and this regarding getting involved, and there are some great responses there, but I'm wondering specifically about the range of roles available within open-source projects. Are there opportunities for my additional interests in interface design, usability, etc. and how do these aspects mesh with the open-source contribution process in general?
Edit: I didn't intend to emphasize my age (I'm not all that young anyway :) so I removed that for clarity. For the purposes of this question, I'm interested in the UI and usability aspects of open-source projects and how I might contribute to those aspects in addition to programming contributions. Thanks for the responses so far.