These are the deductions available under section 80D:
Premium paid for health insurance and preventive health checkup: One can claim deduction up to Rs. 25,000 for health insurance premium paid for self, spouse and dependent children.  If either of you or your spouse is a senior citizen (>=60 years), the deduction limit goes up to Rs.50,000.You can also claim deduction up to Rs.5,000 for preventive health checkups for self, spouse, and children.

However, the total tax benefit is limited to Rs.25,000 or Rs.50,000 as the case may be.
If you pay a health insurance premium for your parents you can claim the additional benefit of Rs.25,000 per financial year. If either parent is a senior citizen the limit goes up to Rs.50,000 per annum.

However, payment is to be made through banking channel (Cheque, demand draft, credit card, debit card, net banking, etc.)
Medical expenses for uninsured senior citizens: If you are a senior citizen (>= 60 years) and have not purchased any health insurance, you can avail deduction for medical expenditure incurred up to Rs 50,000 per financial year. This rule is applicable to FY2019.

However, please note the total deduction that can be availed for health insurance, preventive checkup, and medical expenses shall not exceed Rs 50,000 (from FY2019). Additional, you can also avail of this benefit for payment towards the medical expenditure of your parents provided they are senior citizens and have not purchased any health insurance.