What is the average time it takes for a child to outgrow a dairy allergy?

A year or longer: Dairy allergy comes in a few flavors. A number of babies can have a cow's milk intolerance or even a mild to moderate milk protein allergy that lasts approximately a year or so, then resolves. These are the kids on soy formula who do fine on whole milk at 1 year. Others have a real milk allergy that can persist several years. If lucky, they outgrow it by 4-6, but some continue for many years.

Milk protein allergy: Milk protein allergy is more common before the age of 2 years. Most children tends to outgrow after the age of 2 years, although some persists.