Yes, you can buy life insurance on your mom if she gives her permission, and you can afford it.
In order to buy life insurance on another person, you need an insurable interest in that person, meaning you stand to lose financially if that person were to die.
There does exist an insurable interest between spouses, parents and their children, siblings, and business partners, among others.
So, you may be able to purchase life insurance on your mother, but you will need her permission, she may need to sign the application, and she will probably have to answer some health questions, and/or take a physical exam.
There are some life insurance plans for people age 78 and under which do not require a medical exam.
Here's how you can learn more about life insurance for people over 60 to help you find affordable life insurance for your mother.