Your data is telling you what you need to know about turnover and age
To really grasp a free/open source software project, you need to know how the community that develops and supports it is evolving. Attracting lots of new members will be a reason for celebrating success in a young project — but you should also check whether they stick around for a long time. In mature projects, however, you can afford not attracting many new members, as long as you are retaining old ones. The ratio of experienced, long-term members to recent ones also tells you about the quality of the code and need to support members.