Can’t Enable Apple Watch Auto-Unlock With macOS Sierra installed on a Mac from at least 2013 and an Apple Watch (the very first one), users should be able to unlock their Mac with their Apple Watch. I have an Early 2013 MacBook Pro and an Apple Watch, both of which have the most updated version of the OS installed. I followed these instructions to get it to work (checked 2 factor authentication is on, I have a password on my Watch), but I do not see the option to use my Watch to unlock under System Preferences. Any ides on why it does not work? Could it have something to do with me having 2 Apple IDs, one for iTunes and one for iCloud? Could it be my Mac is somehow not ready for this feature (although it is from 2013)?
Are you seeing the "Allow your Apple Watch to unlock your Mac" checkbox?

You may need to enable Continuity.  Make sure both devices are on the same WiFi network, and Bluetooth is enabled.  The article also had an error, it says 


  "[...] make sure that Disable Automatic Login is unchecked. If the
  option is grayed out, you might need to click the padlock icon at the
  bottom of the window to make the necessary changes."


I think they meant that the box is checked.

EDIT: Here's the Apple article you want to reference: https://support.apple.com/en-ca/HT206995