Asthma can go undiagnosed in elderly people for the following reasons:

• The diagnosis is difficult because symptoms of asthma may resemble some other problems like cardiac or other lung diseases
• Older people are often on several medications. Some of these medicines may trigger or worsen the asthma. Medicines like aspirin etc. given to relieve pain, beta blocking agents given for heart disease or high blood pressure and beta blocking eye drops used to treat glaucoma can worsen existing asthma.
• Symptoms of asthma in elderly people:    
• Difficulty in breathing.
• Persistent and unceasing cough, especially at night.
• Wheezing or shortness of breath especially during the night.
• Difficulty breathing with severe tightness in the chest

What can you do to prevent asthma attacks?

You should keep a record of things that trigger asthmatic attacks.
Before using any medicine for any other condition, ask your GP if it has any effect on your asthma, or if it may trigger asthmatic attacks.