It really doesn't, RiAnnon.
I think she avoids it, actually. She makes a big distinction about "skill level" - that just b/c a child is x-age doesn't mean s/he'll be able to do the various things if s/he hasn't been taught and internalized them. The closest it's come is that there's one skill per year of age and that this is a very gradual process. I think she's more concerned about skill development rather than age. The examples in the book are a wide variety of ages and sometimes the child just has a name and no age.
For me, I'm finding having read the book when she was age 2 kind of laid the foundation in my mind but she was still too young for many of skills except the most easy and physical ones. Reading it again I'm picking up more of the philosophy and plan to follow the teaching (like in the post I did just above) more thoroughly, practicing, etc. Before I just mostly told her choices.