The age for housebreaking varies from dog to dog. It has as much to do with how we train them, and how attentive we are to their needs. In addition it also depends on how much time you have to spend with them.
Everything else being equal, a dog that isn't left alone for long periods will probably be housebroken at an earlier age. The trick is to get them to go out before they get desperate.
Frequent potty breaks with plenty of praise when they do their business in the proper place encourages and teaches them where they should "go".
We got Indy at nine weeks of age. Within a few days he was beginning to go to the door to be let out. This is where paying attention to him was critical. If we noticed him quickly enough, he would go outside in his fenced area to eliminate his wastes. If we missed his signal, he would have an accident.
By the time he was twelve weeks old, accidents were rare. I would say that by 14 weeks, he was completely reliable. If we didn't see him at the door, he'd either whine, or give out a small bark to get our attention. If that failed, he'd find us, then lead us to the door.
It may have been even quicker than that, but I'm confident that it was within that time frame. Had we not been as available for him, his training would have taken longer.
The truth is that a dog's housebreaking depends as much on its owner as the dog. With patience and diligent attention to your dogs signals, he'll quickly learn the rules of the house.
Tom