It runs in my husband's family. He was 6 when he was dry at night, but his brother was 12! A nephew was 11. So I didn't bother with training my eldest son, who had a full nappy / dry night every night. I thought it will come when he's ready, so better not stress about it. Otherwise I (and he) might have six years of stress if he isn't ready till he's 10 or so...
Then, when he was about 8 years old, I heard of the Rodger system.
It is a device that you clip on the special Rodger pants. When it comes into contact with urine it sends a signal to an alarm which is plugged in the mains. This wakes the boy (or girl) up, the very moment he starts to wee. He then has to get up, recognise he needs a wee, turn the alarm off, and go to the toilet.
Lots of people were raving about this system, but I thought, I bet he is the only one with whom it doesn't work. But no, it was fab! The first few days he didn't even wake up, and we had to wake him when the alarm went. Then he started to wake up when the alarm went, and did have wet pants, but did not have a wet bed, which is a great improvement in my books! Then he started to wake before the alarm went, and eventually he didn't wake at all or wet himself!
It was around 10 day when he had his first complete dry night, and they say that when you've stayed dry for 2 weeks, you're officially dry. This was after six weeks with my son, and we haven't looked back since!
Look at bedwettingalarm.co.uk