On the 9th of February 1998 Bruce Perens published the Open Source Definition and made the public announcement of the Open Source Initiative that Eric Raymond and him were starting. Friday, February 8 was the last day of Decade Zero of Open Source. Saturday, February 9 is the anniversary of Open Source and the start of Decade One.
You can read his article about the state of Open Source here.

Open Source is 10 years old . . . , well I hope that it is refrigerated, because once I left an open source on the table, and it went off after only 2 days, granted it was hot climate, but 10 years is a bit long I think. It's always best to refrigerate your source after opening it.