Senior citizen health insurance - 78 years old parent coverage

I want to buy health insurance for my father who is 78 years old. He has diabetes and asthma. Most insurance companies are either rejecting the application or asking for very high premiums of 25000 per year for just 10 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, Max Bupa, and Religare. 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.