T.S.
It is NOT silly to take him to the doctor. He is a different PERSON, you can't just assume he needs the same treatment! His symptoms seem the same to you, but you aren't trained to listen to his lungs etc.
Aside from it being totally illegal to give a prescription drug to a person for whom it's not prescribed (come on, it's not like you're talking about Tylenol here... Albuterol is a real drug). Dosing isn't like cough syrup... there isn't a set does for a certain age. There are a number of factors that DOCTORS take into consideration when establishing dosage.
Call the doctor, make an appointment, get a treatment plan for HIM.
If the Rx ends up exactly the same, you can decide whether to fill it or not (although sharing an inhaler seems like a great way to keep everyone having the same symptoms all the time kwim?)
HTH
T.