according to mims the ff is the dosage for salbutamol
Acute bronchospasm
Child: 1 mth-2 yr: 100 mcg/kg (max: 2 mg), 2-6 yr: 1-2 mg, >6 yr: 2 mg. Doses to be taken 3-4 times daily.
from here we will see that it may be used for 1 month old.
IMPORTANT: consult your pediatrician before using this drug as it may have side effects on your baby so that proper precaution will be taken.