Senior citizen health insurance - 65 years old parent coverage

I want to buy health insurance for my father who is 65 years old. He has thyroid and asthma. Most insurance companies are either rejecting the application or asking for very high premiums of 40000 per year for just 5 lakhs coverage. Is this normal for senior citizens? Are there any specialized senior citizen health insurance plans that are more affordable? I have checked HDFC Ergo, ICICI Lombard, and Aditya Birla. HDFC Ergo is asking for medical tests before approval. Will the pre-existing diseases be covered? What is the waiting period? Please suggest the best options for insuring elderly parents.