My daughter who is thin and not really developing started wearing one last year as a fourth grader. It was a nipple thing not a **** thing. Wow, that sounds weird! But in some shirts you could see the outline of her nipples and that was that. Most all of her classmates started wearing them in 3rd or 4th grades. I simply called them undershirts because dd seemed at first to be upset I got her one. Altough it was just the girl sport bra type thing. I bought her some of those and a few camisole type cotton undershirts and let her choose.
To me there can be no set age, I have known girls as young as second grade who wore them and others (like myself) who got one for junior high because it was too humiliating not to wear one!
As hard as it is, you have to throw out those preconceived notions of what other girls, yourself, your sister, etc., did/are doing. Its all about the individual girl. I think if your dd is ready, then the time has come!
Oh and for deodorant, use your nostrils and also look for sweat stains on white clothing. I say 10 is the latest you should wait for that, I know when I volunteered in my kid's 4th grade classes, it frequently stunk! But never smelled a thing in the years before that. I would rather err on the side of caution with that one. I would be mortified if somebody every thought my child smelled bad.
Oh and I have to vouch for the Care and Keeping of You. That book really helped my daughter and me come to terms with what lies ahead! And they have several other books about friends, self image etc. They are all really helpful for girls that age. The whole series was recommended by my pediatrician, I wish they had something like that when I was her age. Beats finding out all the wrong info from word of mouth from other girls. Which no matter how hard we moms try, the rumor mill is always working overtime!