Since Mavericks (I believe, could have been earlier) the extended support window is 3 years. Mavericks ended in 2016, Yosemite in 2017, El Cap in 2018, and Sierra in 2019. Unfortunate, but Apple has never really supported their older OSes for very long after a new release.I noticed I didn't get any security updates lately. Sierra is only 3 years old, shouldn't OS be supported at least 5 year?
Microsoft supports Windows up to 10 years!