Re: ages and food
I have a good handout from Heinz on introducing foods. It shows what to start as beginner foods, what the strained (stage 2, 6 months) foods are, junior (8 months), and "toddler" foods (12 months +) are.
Besides food like that, I think it all depends on the baby. DD is 6 1/2 months old and has sucked on a pickle sliced lengthwise (stole from my plate at a restaurant), tried eating those baby rice rusk cookies, as well as finished all the beginner foods and is going to start on "stage 2" soon.