Q: Cant see 2 factor authentication option

I am a long-time Apple customer with many iOS and OS X devices.  I also do not have two-factor authentication available to me.

I believe the reason in my case is that I have been using two-step verification, a slightly older security enhancement that provides even more safeguards than two-factor authentication.

Another possible reason for not seeing two-factor authentication would be not having a valid credit card on file for your Apple ID.  Here is Apple's writeup on the subject:

Availability of two-factor authentication in iOS 9 and OS X El Capitan - Apple Support