Ofcourse there are limitations to get insured after certain age as most plans in India stops intake at age 65 or max by 75 yrs. But that doesn't mean 'zero' chance, there are plans by HDFC ERGO and Care Health where they can be insured at any age.
Depending on the medical history, the suitable plans may vary. For instance, as per your details, they can still apply for HDFC ERGO's My Health Suraksha, which is the best possible plan in terms of coverage and value for money. In case of rejection during medical screening, you can try with the next suitable insurer, though the features may vary you can still get decent coverage.
If you wish to discuss this personally, message @ wa.me/919846233161