My DS1 I found very hard to toilet train as he has autism (was not heard of then, but now I realise his problem) I got him potty trained by two and a half.This was helped by the fact that I was pregnant with his younger brother at the time and was not looking forward to washing and drying double the amount of Terry nappies when the baby came.DS2 was completely different, he just about toilet trained himself as he could not tolerate being in a wet or dirty nappy for long and, as soon as he was able, would try and remove it.
My mother, who had five children, thought it a disgrace for a child to be in nappies at 18 months!
My grandchildren and great grandchildren seemed to take longer but I put that down to modern parenting and did not interfere.