Will My Older Mac Run Yosemite?

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In respect to this, is OSX Yosemite old?

OS X Yosemite was announced and released to developers on June 2, 2014, at WWDC 2014 and released to public beta testers on July 24, 2014. Yosemite was released to consumers on October 16, 2014.

Beside above, can you upgrade from Yosemite to Sierra? If you have macOS Sierra (the current macOS version), you can upgrade straight to High Sierra without doing any other software installations. If you are running Lion (version 10.7. 5), Mountain Lion, Mavericks, Yosemite, or El Capitan, you can upgrade directly from one of those versions to Sierra.

Keeping this in consideration, can an old Mac be updated?

Mac updates its macOS (previously Mac OS X) desktop and laptop operating system once a year, like clockwork, bringing new features and improvements. That's all very well, but the latest version of MacOS, known as Catalina, won't run on any Mac older than 2012, and in the case of the Mac Pro, late 2013.

Can you update from Yosemite to Catalina?

If you're using one of these computers with OS X Mavericks or later,* you can install macOS Catalina. Your Mac also needs at least 4GB of memory and 12.5GB of available storage space, or up to 18.5GB of storage space when upgrading from OS X Yosemite or earlier. View the complete list of compatible computers.