What is the maximum ht of a main disconnect and where is it in the code?

6' 7" to the center of the grip when in its highest position. 404.8(A)

How about a meter?

Deck extends out 5', 4' high (bottom of the joists), 2" out the top thru the deck floor to the WH.
No lattice or other obstructions.

(NH) would this be a utility call or AHJ,Code etc.?

Not done, but the question was raised by the home owner.
We're in the building stage now. wrap around deck, No need for it, but the HO wants the extra 3' of deck.

Many AHJ and utilities consider the meter as electrical equipment subject to 110.26 Clear work space.
The utility will be the ultimate judge of location for a meter and may require it to be moved.
When people come in for their building permit for a deck the first question we ask is where the gas and electric are located. Firemen do not like to climb under a deck to shut off gas and electric when there is a fire.

Thanx, My advice was against it, I figured the work space.
But with enquireing minds I don't want to give a bad answer and have them get the info and think I gave a line of "stuff".

Consider the language of 110.26 "likely to require examination, adjustment, servicing, or maintenance while energized".
I think service equipment should always qualify.
They are not going to drop the primary fuse on the transformer if they open the meter can.