I googled "psychological development nine years old" and found the following:
"The nine year old's appetite has evened out. The huge appetite of some eight year olds has moderated, and poor eaters now eat more. She is interested in food, cooking and eating it, and usually comes home from school ravenously hungry. She still has difficulty with table manners and remembering to wash before eating. She knows what is expected at the table, just doesn't always remember to do it."
Why is nine female?
"Nine is a good sleeper, but some do have nightmares.Ten hours of sleep is still recommended for nine-year olds.
The nine-year-old child is not very neat with her clothes, rarely hanging up coats or putting dirty clothes in the hamper without being reminded."
Apparently this can persist through her 36th year.
"Some will pick up dirty clothes from the day before and try to wear them, not really noticing whether clothes are clean or dirty. Therefore, nine still needs help organizing her clothes and dressing routine."
Back off, About.com
"Nine likes to plan his days, and is persistent in completing his plans. Parents can enhance nine's emotional sense of security by encouraging this planning urge, talking about the family's plans, and helping him to organize his days."
ok..suddenly, when it comes to organization and persistence, Nine is male. Well then, Happy 9th Birthday, little transgendered robot.