What is an appropriate age to start guitar lessons for a child?

There isn't necessarily a particular age that a child should be before starting guitar lessons. It is also a different situation for every child, but it is important for the child to have an interest in music and for them to actually want to play the guitar before trying to force it upon them, as they will be more likely to resent the parents or teacher if they don't want to play. Therefore, an appropriate age would be when they are able to learn efficiently and also when they develop an interest.