The right age to start is related to the instrument you choose and your child’s interest in music. Mozart was playing the pianoforte at 3 and composing at 8, but not too many of our children can hope to achieve that.
As for the instrument, it’s pretty much up to the parents to make that choice. I don’t know your son’s age, but any request he makes will be limited by whatever exposure he has to different instruments.
In terms of instruments for “real” music, the piano and violin are the most likely candidates. Before age 9 or 10 children don’t have the wind power for a wind instrument (“The Music Man” notwithstanding). You can forget about guitars and other plucked string instruments until the child’s hands have achieved almost adult size and strength. The purchase of a piano for a child who may prove to have no interest in it can be an expensive bit of frivolity, unless the parents themselves want it.
However, one can now buy digital keyboards, some with less range than the piano and some with the full 88 keys, for reasonable sums. One advantage of those instruments is that the volume can be turned down if the parents would rather watch the evening news while their child struggles with exercises and simple compositions. A disadvantage is that, in a way, keyboards seem more like toys than serious musical instruments. Sometimes children merely want to bang on them rather than study them. Incidentally, most piano teachers say that children should begin taking lessons around 7 or 8.
Now for the violin. There is much more information available about young children and the violin, thanks to the work of a fantastic Japanese musician and teacher named Suzuki. You may have heard of The Suzuki Method and the hundreds of thousands of children as young as 3 who have learned music from it. Professor Suzuki discovered that, if you gave very young children an instrument tailored to their small size, they could become quite skilled on the violin. Furthermore, studies done on children who had participated in such training showed that they often excelled academically over their untrained peers (although the available research doesn’t account for such factors as family income, education and parental motivation). Frankly, I don’t know why no one has promoted a keyboard designed for small hands and short fingers. There are some in existence, but they’re hard to find. And most teachers prefer to have the children wait until they can manage keys of a standard size.
Now I’m going to give you my personal opinion. If you can afford the outlay, go with the piano. Although former President Clinton continues to play the saxophone for his personal enjoyment, it is mainly the piano that allows for continued individual pleasure. For all other instruments (with the possible exception of the guitar), you almost have to have someone on another instrument to play along with you. The piano can provide group or individual enjoyment for many years and offers the best possible introduction to harmony and rhythm. I speak from experience because, short on both talent and training, I play my piano almost every night, all by myself. And I love it.
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.