Over time
Visualizing Code Repositories Metadata
The code repository that builds this page
Count of Repositories Created Over Time
Count of Repositories by Last Update Date
The fact that NASA has repositories created in the older years but that doesn't show up much in those same years for "last updated" would seem to suggest those early repositories tended to stay active.
On a proportional basis, HoustonDataViz has far more repositories last updated only shortly after their creation, which makes since as those repositories tend to be demos, data jams, presentations, and other short-lived repositories tied to events.