What age do you have to be to use bicarbonate (sodium bicarbonate) of soda in your teeth with a toothbrush please tell me?

Ask your own dentist: I don't think that you should do anything on your own without the asking the dentist who personally treats you. Ask your parent to call or the next time you visit the dentist. In the meantime use regular fluoridated toothpaste and also floss your teeth. If you don't know how to floss, ask your dentist or dental hygienist to show you how.

There are some: Commercially available brands of baking soda toothpaste that are safe. That would be a better alternative than a home made remedy. Hope this helps.

Not at any age: You should not use bicarbonate (sodium bicarbonate) soda to brush your teeth with at any age ever.. As these might ruin you teeth enamel from the high abrasive contents of the soda.. Use toothpaste ;).