Get them a set of morals, don't lie, cheat, steel, etc. And get them a Religion. But when you are potty trained is not going to change the person you will be later. The age that the child develops control over the muscles and can go on the potty is a development like sitting and walking, and you will find a bell curve like that for all development stages. Many 3 year olds walking down the mall with diapers on below their pants and you don't know it.
Girls train earlier.
Girls go through puberty at 9 and boys at 14, a 5 year difference. So girls train around 2 yr. I've had a few patients going on the potty before 18 months and a few over 4 years old. Also males can be urinating on the toilet at 2 and not poop on there till over 3. Males have a harder time pooping.