At what age do we have to brush the baby's teeth?

My son is 6+ months and he has not teeth yet so haven't started any tooth brushing for him. I am using NUK's mouth wipes to clean his gums after meal & before sleep. I will only be starting brushing once his teeth has sprouted and is visible. Once my baby's has sprouted, I will be using a finger toothbrush as my other mummy friends have warned me and advised me that it's less of a struggle to use a finger brush rather than an actual toothbrush. Meanwhile, I let my son gnaw on teething toothbrush in the shape of a banana! And he super loves it. I got it at Kiddy Palace at about $15-$20. Here's an article for tips on caring your baby's teeth. http://www.parents.com/baby/health/baby-teeth/baby-tooth-care-tips1/