Basically, anyone with an insurable interest in another person may buy life insurance on that person.
An insurable interest means you may stand to lose financially if the insured person were to die.
People with insurable interest in one another may include spouses, siblings, parents and their children, grandparents and their grandchildren, business partners, etc.
For instance, you may rely on your grandmother for financial support, or you may have to pay for your grandmother's funeral if she were to die.
In order to buy life insurance on another person you will need your grandmother's permission, in addition, she will have to sign the application for life insurance, and she may need to answer some health questions, or take a physical exam.
Globe life Insurance offers simplified life insurance for people age 78 and under with no medical exam required.