bio yoghurt is ok from 6 months as long as it doesn't state otherwise on the label. From the Food Standards Agency:
'Bio' yoghurts usually claim to contain 'live' bacteria, or 'cultures'. In most products, these will be the same types of bacteria that are found naturally in a healthy person's digestive system.
So babies don't need to eat bio yoghurts to get these bacteria. But if you want to give bio yoghurts to your baby after he or she is about six months old, this should be safe, as long as it doesn't say on the label that the product isn't suitable for babies.
Your baby needs plenty of energy to grow, so make sure you give him or her full-fat varieties of dairy products such as yoghurts and fromage frais. Remember to avoid using cows' milk as a main drink until your baby is one year old.
If you would like more detailed information about a specific product, you can get in touch with the manufacturer.