How to calculate age in NUMBERS

> I am guessing it's going from my computers calendar?

Right. TODAY() is based on your system's clock.

> Are all apple computers sync'd to the right date/time?

That depends. All MacOS systems for years (decades?) now have supported NTP, the internet-standard for time synchronization. All systems are configured to use NTP by default, synching to Apple's time servers (time.apple.com).

However, individual users can override this via the Date & Time options in System Settings (or System Preferences on older OS versions). You may work for a company that maintains their own time servers, or you may prefer a public time server, or you may turn off synchronization altogether if you want.

> could there a possibility that their computer messes up the years because their computer clock is off?

Their clock would have to be way off to affect this type of calculation.

NTP generally keeps systems in sync within a few milliseconds. For it to be off by months - or even hours - would be extreme.

> Or are all Apple computers constantly sync'd to the clock?

They are, as long as the user hasn't overridden the system configuration to turn off synchronization.