I'd say, generally, with consistent training, most dogs become fully potty trained (more or less) by 1.5 years. Many are trained well before 1 years old (maybe they're just lucky?). Some are not well potty trained beyond 2 years old (maybe the training wasn't consistent?).
If you're persistent and prevent accidents whenever and wherever possible, I'd say after 1 years, they should be potty trained (but may still have accidents).
For Scottie, by 1.5 years he was quite reliable. By 2 years, he was fully reliable. I very gradually let him have more free-range access as I saw how he progressed. Accidents-prevention is key!
