The 15th anniversary of the release of Mac OS X 10.0 was yesterday.
Technically, Mac OS X is 17 years old since Mac OS X Server 1.0 was released on March 16th, 1999
Basically, the release of OS X 10.11.4 is farther away from Mac OS X Server 1.0 (17 years, 5 days) than Mac OS X Server 1.0 is from the release of System 1 (15 years 1 month 20 days).
Here’s to the crazy ones: a decade of Mac OS X reviews • 2011 May 12 • John Siracusa • Ars Technica
Tangentially related, Apple has stuck to one architecture for about 12 years on average.
They used the Motorola 68k family from 1984 to 1996 and Power PC from 1994 to 2006. They’ve only been using Intel since 2006. It doesn’t really seem like there are any new architectures on the horizon, unless we’re talking about Apple someday completely transitioning to ARM.
List of Macintosh models grouped by CPU type • Wikipedia