I know that in dogs, leg-lifting is a fairly macho thing and a sign of coming of age. This is a recent development for a couple of male coyote pups I have been observing. These pups were born in the Springtime of 2009, so they are about 16 months old. I don’t know if this is the time frame for dogs, but it is what I have observed in two young male coyotes. Before this recent development, all four legs were firmly planted on the ground, with a minimal “squat” in the back legs.
Females normally squat low to urinate or mark. However, even females sometimes lift a leg, but it is done a little differently than the male: see last photo in posting “Mom by Charles Wood” on August 1, 2010. The female will swing the leg more forward and will retain a squatted position vs. the male whose leg goes out to the side.