Oh my gosh, I never knew so many people had the same problem as me:) I started when I was about 5, craving dirt, but I rarely could find the right kind of dirt I craved. I felt desperate, then I discovered chalk, it was irresistible, and then I discovered baby powder which was even better. And, I found out a few months ago that I'm anemic. I'm now 18 and still eat baby powder, I love it, I don't think I ever wanna quit.
And, btw, I've even had the same tub full of baby powder fantasy for years!