There does exist insurable interest between a father and son, so you could buy life insurance on your father.
However, in order to buy life insurance on him you will need his permission, his signature on the application, and he may need to answer some health questions, and maybe take a paramedical examination which is paid for by the life insurance company.
If you are buying the life insurance you would be the owner of the policy, and responsible for paying the premiums. Also, you would want to name yourself as the beneficiary of the life insurance, so if you father were to die, you would receive the death benefit from the life insurance.
Here's how you may buy life insurance online to provide life insurance protection on your father.