it's individual.
my late love (a gsd mix, he was ten when i got him), asked once or twice a week. sometimes every other week, he became a couch potato once he found out what a couch even is.... heats of my or other gals in the vicinity didn't really faze him.
my current boy (a leonberger, three or so years old. his previous "family" wasn't very clear about his age) is usually up for some fun once or twice a day. when my or other girls in the neighborhood go into heat it spikes to six or more times a day. good thing their cum doesn't stain during that time.