I think my lab was like 18 months when we did it. Probably waited a bit too long. He still has to piss on every mail box and every weed or clump of grass that is a bit taller than its surroundings. He definitely became less interested in other dogs and started listening better. As for energy, well, he's a lab, so he goes ape shit daily and in the field, he can't be stopped, even at 8 years old.
Unless you plan on studding, I'd say it's worth doing, if for no other reason, you don't have to worry (as much) if he gets out and roams the neighborhood.