Our allergy/Asthma doctor is a bit different. For logical reasons (too long to discuss agian) they don't diagnose asthma until the child is old enough and able to do a pulmonary function test and they can decide if they have a decent chance of outgrowing the asthmatic symptoms. They still treat it with asthma medication and such but call it reactive airway disease (RAD) until the child completes a pulmonary function test. Danny is 4.5 (still considered RAD) and was diagnosed with RAD at 2 months old. Danny is VERY different though. He is on Singulair (5mg), Symbicort, Flonase, and Afrin daily. He is also on Proair (his rescue inhaler) twice daily. They are unable to control his breathing any better than that at this point. He also has prednisolone (oral steroids) on standby at home for an 8 day course when he is on nebs at least every 4 hours for more than 48 hours or anytime he needs them more often than every 4 hours for at least 12 hours. As soon as he starts coughing or getting a runny nose we have to start nebs. Even with starting nebs with a runny nose, it will usually progress into a sinus infection needing at least 2 rounds of antibiotics and nebs every 2 hours for 2 weeks in addition to 8-11 day courses of steroids. :/
Like I said...he is VERY different... I think doc's usually suggest starting them only if the child is wheezing or having an asthma "attack" (what ever form of attack your child has). One of the other moms on here could probably help more if they get on here soon but I didn't want to just leave you without ANY answer.