What's the earliest model of the MacBook to support Wi-Fi networks over 5GHz?
All MacBook models have shipped with support for 5GHz Wi-Fi networks since their first generation.

802.11a


MacBook (2006)
MacBook Pro (2006)


802.11n (including draft-n)


MacBook (Late 2006 thru Mid 2010)
MacBook Air (2008 thru Mid 2012)
MacBook Pro (Late 2006 thru Early 2013)


802.11ac


MacBook (Early 2015 thru Mid 2017)
MacBook Air (Mid 2013 thru Current)
MacBook Pro (Late 2013 thru Current)


802.11ax


(None yet)


Reference: https://everymac.com/systems/by_capability/macs-with-airport-airport-extreme.html