Will my 2013 MacBook Air be able to use macOS 12

Big Sur is the latest version of macOS you can run.

How to get old versions of macOS - Apple Support

Dwill78 Said:

"Is my computer useless if it this old. Or can the new system be installed"

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Edit:

A. Get the Installer for Sierra Here: macOS Sierra - Apple***

***Source: How to Get Old Versions of macOS - Apple Support

Dwill78 Said:

"Is my computer useless if it this old. Or can the new system be installed"

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Yes. See Here: macOS Sierra - Technical Specifications - Apple Support

Installing this:

A. Get the Installer Here: macOS Mojave - Apple

B. Important: Backup your Mac First

Be certain you create a backup of your Mac prior to performing this. That way, you will have something to restore your Mac from, should anything go wrong with the configuration. For the Backup, use an external hard drive of at least 1.5 times the storage, or use iCloud.