However, in order to buy life insurance on another person, you must have the permissions permission and signature. Also, a person being insured may need to answer some health questions, or even take a physical examination when you apply for life insurance on the person.
In order to buy life insurance on another person there must exist Insurable Interest between you and the person you want to insure for life insurance.
Insurable Interest basically means you stand to lose financially if the insured person were to die.
Usually, there exists insurable interest between spouses, parents and their children, siblings, relatives, and business partners, among others.
Here's an article explaining What is Insurable Interest?