There is no set age for a child to start learning music. There are a number of factors involved in determining when your child is ready to start music lessons:
 
- Overall maturity level of the child: some kids happen to have a good level of concentration and patience at an early age; it is easier to start music lessons with such students, than the ones that are “all over the place” and have no patience to sit down even for one minute. The child should not be forced into sitting in long sessions; it will only back-fire. Your child will eventually grow up and have patience, so don’t rush to do it too early.
 
- Physical conditions of your child: certain instruments demand certain physical abilities; in general it is not a good idea to start playing wind instruments at a very early age, especially the ones that command major pulmonary power, such as the trumpet or the trombone. Other instruments, such as the piano, that come in only one size, may be too demanding for a child whose hands are too narrow, or the fingers too soft and not developed yet (opposite to contrary believe, it is not the length of the fingers that is important in playing the piano, but the width of the hand and the horizontal stretch of the fingers)
 
Considering the above points (and probably others), in general the ages of 4 to 7 are the common years for a child to start learning music. If one starts music lessons at too early an age, or pre-maturely (i.e. an older child that is very impatient), you run the risk of making very little progress and result in the child’s and the parents’ frustration and the ultimate abandoning of this activity. The risk of starting too late (e.g. 15 years old) is that the child has already developed a certain level of stubbornness and preference of doing “fun” things, and is likely not to want to sit down and practice seriously. Of course there are exceptions in both cases.