Adult children have an Insurable Interest in their Father, which is required in order to buy life insurance on someone else - you must have an Insurable Interest in the person you wish to insure for life insurance.
That means you either rely on the person for some means of financial support, or that you would suffer some financial loss or cost should that person die.
Many adult children buy life insurance for their Father to make sure there are funds available to pay for their Dad's burial, funeral, and other final expenses.
Learn more about getting life insurance on your Dad.