can a woman produce children 20 years apart ?
example 29, 17, and 9 ???
Yes, very easily. My extended family and friends are full of large families where the oldest and youngest children are more than 20 years apart. My mother and father both have aunts and uncles that are younger than them because of this, and a very good friend of mine has a biological siblings that are 20 and 24 years older than her (same mother and father). And there's even a TV show about a family (the Duggars) with 19 children. The oldest and youngest are close to 20 years apart.
Think about it, if a woman gives birth when she's, say, 17 or 19 years old, she can easily still be fertile at age 37 or 40 or even older to have other children.
I could certainly have children 20, even 25 years apart if I wanted to. Not that I want to though! I was 20 when DD1 was born, 10 years later, I am 30 and she is 10. We've completed our family a couple years ago after 4 children. I've known several families that had adult or older teen children and then had a baby as well, it happens.