As a quick post, I am presenting my table here of typical Fedora lifespans.
Surprise, surprise — or, if you prefer, surprisingly — over the years, on average Fedora has actually been doing a good job of keeping to what is colloquially described as a 13 month lifespan, despite fairly variable lifespans of almost +/- 20% compared to average as of Fedora 16, often being delayed by a week or two or more, and in the case of Fedora 18, by two months! In fact, it has been keeping to this average rather closely — as of Fedora 16, the cumulative averages have kept to less than 2% from the overall average since Fedora 5. Well we’ll see how that affects things, as it is right now I’ve estimated the lifespan of Fedora 16, which I’ll correct when the official number comes out. We’ll see how the two month delay has/will affect(ed) the scheduled release of Fedora 19, and as the case may be Fedora 20 and so on.
Each of Fedora’s End of Life (EOL) is scheduled at a month after the release of the second version of Fedora after, eg. Fedora 12’s end of life was one month after the release of Fedora 14, and so on.
So, while I’m making this up, if the lifespans of Fedora 1 and Fedora 2 are any indication, Fedora presumably only started with the “every six months or so release dates” and/or defining the EOL as one month after the release of the second version following a given release, somewhere around Fedora 3, or possibly Fedora 4. (Although apparently Red Hat Linux, as mentioned here, had a release schedule of about every 6 months, too — and an erratic lifespan of 18 months or 3 years or 5 years, depending on what appears to have been whim though what probably was more along the lines of support contracts tied to specific releases, public reception to a given release, or a given release’s perceived technical excellence and value, etc.)