Here at Music Scene one of the most common questions we get is "what age should my kid start learning an instrument?"
Ages - 1 to 3 Early exposure to music
Ages - 5 to 9 Begin learning an instrument (Piano most recommended, guitar, ukulele)
Ages 10 and up - Learn any instrument they may be interested in, and perform at a proficient level.
There is definitely no definitive age a child should start this process. As a parent you must ask yourself what is the goal of these music lessons for my child. If your goal is to get them involved in music early, because of the benefits it has on the brain, then you may expose your child to music at the early age of one. Beginning with very informal "music lessons," such as just playing music around them.
By the time a child is 5 years old they should be ready to start learning an instrument (we recommend starting on piano). Typcially at this age it is still going to be difficult for them to perform the instrument at a high level, but the lessons still can be beneficial. A child can start the beginning processes of note reading and hearing melodies, and learning basic rhythems and even doing them on their own. Other instruments still can be started at this age such as ukulele, drums, guitar and the child still can have great success.
Once a child is 10 they now have enough skill to play any instrument that they are interested in. At this age they can now perform their instrument at a proficient level if they practice consistently for a few months. They are also big enough at this age to be able to play the large and more physically demanding instruments (guitars, brass insruments, and drums etc.)
With just about anything there is definitely outliars. Some children learn faster at a younger age, and some can be exposed to an instrument younger than others, and some may need more time.