You may need to wait a few years before you're old enough, but you could start working as a page part-time depending on how your local library hires people. A page works for only a few hours per week and learns the basics like how to properly sort and shelve books. At my library, we also wash all books that are returned, because people often get the covers dirty. Our library is small, so jobs here start with "circulation assistants" who check books in and out to people. This is also a part-time job. I know people who started as pages in larger libraries in our district and are now working on all kinds of interesting projects like teaching after-school science classes to kids and running special technology programs.
RE: I had SO much fun painting at the library!! ♥ Take a look!