Brushing question: old toothbrush? or no brushing?

Replace your toothbrush every 3 months. See the dentist for a cleaning every 6 months and they will give you a toothbrush as part of the price. Also toothbrushes are only like 3 bucks or less, so you could always just go buy one yourself if you are old enough to get to a drug store, grocery store or convenience store.