Go here for example:
https://www.kurnia.com/products-and-service...diguard-premier

Click on MediGuard Premier Insurance Brochure
(PDF, 1525.08KB )

So you see that age 65 is the last chance to start the insurance at Kurnia. Others have different limit.

So you see there is quite a wide range what you can expect to pay. You need to compare.

Note there are some discounts possible. For walk in clients not using an agent it is 15% at Kurnia, that is quite normal.

If you have medical insurance you can add your mom to your policy that usually is worth a family bonus of 10%.

Overall I agree totally with you that it is a great idea to get a medical insurance for your mom. You know the risks already from your dad.