I am 56 years old and had the onset of severe asthma 5-6 years ago. I have been through a lot with my asthma and I have not clue what this doctor is talking about. I would definitely get a new doctor.
What type of symptoms are you having? Why did you get the chest x-ray? And if you have even mild asthma, is he not going to at least give you an inhaler to be prepared in case of an emergency? I would definitely change doctors. If I can be of any more help, feel free to ask. I'm not a doctor, just an asthma patient.