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.
In fact you may want to use reverse psychology between 18 and 24 months by telling them no you can't sit on the toilet. Let the urge to go on the toilet come from the child. 2. hold it back until they get to the potty, and 3. let it go when they get up on there, and do this every day for a week, then they are ready to start going on the potty and wearing cloth pants. So the best advice here is wait. They have total control.