Zora Neale Hurston introduces all of her characters in a rich, visual way that gives the reader a good image of the character. However Hurston likes to leave the reader guessing when it comes to the age of a character she is describing. Very rarely if at all is the reader given the ages of the characters in chapters 1-5. We are left to wonder how old Janie actually is when she is first married, and how much time passes before she meets Joe Starks. Even in Hurston's description on Nanny she fails to give an age and we can only assume from her civil war experiences how old she is. Another important side effect of this age absence is that the reader can only infer the age disparity between Janie and her two husbands.
I think the main reason that Hurston uses this tactic is to make Janie's personal growth a more obvious thing. Since the reader is left in the dark as to how old she is, the reader can see more clearly the psychological changes and maturations that Janie undergoes in her experiences from being a kid to when she is living with Joe in Eatonville. For all we know, Janie is barely into her twenties when she meets Joe as young marriages were more common at that time. This subtle yet powerful strategy is utilized by Hurston to create a more impacting story that the reader can more easily relate to.