CathInfo.com

I think there are several things here.

1)  Prior to the Industrial Age, women nursed their children until about 5 or 6.  Our "milk teeth" fall out when our permanent teeth erupt.  Some children, of course, weaned themselves earlier but it wasn't really weird if they didn't.

2)  During this time, it was also common for entire families to share a common sleeping area.  Sometimes these were separated by curtains, but not always.  It sort of made it really hard for men and women to be intimate all the time.  Planning was essential.

3)  Census records pretty clearly indicate a normal pattern of child birth prior to the 1960s.  Babies came along about every 18 months to 2 years.  I have been doing genealogy for 15 years and I have examined probably thousands of census records and they are all the same--until modern times.

It is pretty clear to me that women used to nurse for much longer than women do now.  Children didn't go off to school or daycare, so there was really no hurry.  Also as children age, they naturally eat more solid food and nurse less.  My daughter is 15 months old and she nurses only 4 times a day now---before we get out of bed, before her morning and afternoon naps, and before bedtime.  

But it seems to me that women's fertility is about the same throughout the ages.  God worked it out so women normally give birth about every 2 years until the Lord sees fit.  It was not unusual in those time for women to have children from the age of 15 to 45.  Really.  The oldest mother in my family tree gave birth at 47 to her 14th child.  And all but one survived infancy.

So, to answer the question---yes, women nursed for 5 or 6 years.  But no, their fertility did not stay at bay for that long.  Some couples, clearly, were not as fertile as others, but generally every 2 years was the norm.

As the 30s and 40s rolled around, though, women were being told to do all sorts of weird things that were unnatural.  Early wave of feminism.  My mother-in-law gave birth to her first child in 1945.  She fed her daughter evaporated milk mixed with Karo syrup.  Can you imagine?  

As for me personally, I have learned that the longer my babies nurse during the night, the longer my fertility stays at bay.  It usually returns around 12-15 months.  The closest space for any of our children is 23 months almost exactly.