Re: has anyone ever heard this?
You need to consult a pediatric pulmonologist if you haven't already.
In our area, some pediatricians and doctors do not like to make a formal asthma diagnosis because they do not want parents to have to worry about pre-existing condition issues if insurance changes. I know of several cases where pediatricians have not diagnosed asthma in children on Medicaid because if they make a referral to a specialist, they lose money (not being able to bill for child's sick visits once child goes to specialist).
Since you are getting conflicting information, please consult a pediatric pulmonologist. If your insurance requires a referral, insist on one being made by the pediatrician or change doctors if they won't give you a referral.
children as young as three do get asthma, regardless of gender.