I went to google and found the following:
"In 1957, studies found that 92 percent of children were toilet trained by 18 months. Today, that figure has dropped to less than 25 percent"
Many years ago both boys and girls wore little dresses and they toilet trained as soon as they walked. Mothers weren't about to wash a pair of underpants every day.
My granddad (b 1902) told my mom about how his mother beat his little brother's butt until it bled because he soiled his pants. Probably not the best way to potty train a child. She was a tiny woman. Guess she was sick of doing laundry that day. My mom said that her grandma even took in laundry to make some extra money.
I don't think 18 months is unreasonable.
It does however take some effort on the parent's part. Some parent's today are not willing to put that time in.