It specifies a minimum height of 42 inches above the deck surface and that is the height you should make your gate.
Building a gate for my deck.
The balusters must be spaced closely enough to prevent a 4 inch sphere from passing between them and the distance between the bottom of the gate and the decking should be no more than 4 inches when the gate is closed.
How to build a deck gate.
We needed a gate on the deck to control the dog traffic.
Banjo short by audionautix is licensed under a creative commons attribution lic.
Hand rails and gates must be at least 42 above the deck surface.
The gate should open onto the deck not onto the stairs.
No gaps in or under the gate can be wider than four inches.