I think there's this mammoth by the name of KO who's working out mighty fine as a 6'5" guard.
Without looking up anymore (since that's a really difficult thing to look up without knowing relative size), Alex Boone was a 6'6" guard and did really well in SF, Le'el Collins is 6'5" and was considered a first round prospect at guard, Mike Pouncey is a 6'5" center and did really well in Miami (still does really well), and Andrew Whitworth excelled at LG for the Bengals and he's 6'7".
I'd honestly guess the average interior lineman is 6'4". While I'm one to prefer a guard/center at like 6'3", there is no hard and fast rule for a lineman cannot excel at guard because of his height. Writing off Hurst purely because he's 6'6" is naive.