A lot of (possibly most?) Julia packages are written and maintained by people who are “X, not a developer”, where X is academic, research scientist, data expert, interested hobbyist, or something else. Very few people in the Julia community are paid for developing software per se.
Most projects welcome enthusiastic contributors and are willing to provide guidance. “Love to work on this” is probably 80% of the required qualifications, you can pick up the rest as you go along.