Whats a good age to start potty trainning? My 2yr old is already wearing a size 5 diaper...

About now. Age 2 is a good age to start potty training. Specially if your child is giving you signals, such as taking of his own diaper or asking to be changed if wet. Remember children learn by association, let him see other people use the bathroom. Be patient, all kids have accidents, they are supposed to, it is a learning process. Avoid pull ups as they are diapers in kids mind. Use training pants.
2 years. 2 years is the average time when children are able to be toilet trained. However, while some children are able to understand what this means at earlier ages, there are plenty of 3 year olds, and even some 4 year olds who are still in diapers. One method is to take a day and just have the child sit on the toilet all day, and when they go, congratulate them.