The source code for StarUML has less than a year of continuous activity, making this a relatively new project.
A short history is not necessarily a bad thing (all projects have to start somewhere!) but it can indicate an immature or volatile project.
A longer source control history would indicate that the project has enough merit to hold contributors's interest for a long time. It might indicate a mature and relatively bug-free code base, and can be a sign of an organized, dedicated development team.
Note: The source code for StarUML might actually be older than the source control history can reveal. Many projects begin by duplicating a large amount of source code from an existing, older project. You can usually tell whether this is the case by looking for a rapid rise in the amount of code early in the project's history.