S.C.
Starting the process of brushing teeth and gums should start as early as possible in my opinion. It helps them get use to having something in their mouth like that and will also help get in their routine of brushing. It doesn't have to be 2 or 3 times a day at this age - just once in the morning of before bed.
My youngest has a horrible gag reflex and I learned this early as a result of brushing his gums. If I had not started so early, I fear he would not be as good at brushing his teeth now when it is extremely important to do a good job.