Yes, if you have an insurable interest in the person you want to insure for life insurance, you may buy life insurance on that person.
Insurable interest means you either rely on the person for some financial support, or you would suffer a financial loss if the person were to die.
Usually, insurable interest exists between spouses, parents and their children, and business partners, among others.
In addition, you may need that person's signature on the application in order to buy life insurance, but that depends on the requirements of the life insurance company.
Learn more about how to buy a life insurance policy on someone else?