Yes. If you are an adult, you may be able to purchase a life insurance plan on your grandpa.
In order for one person to buy life insurance on the life of another person, you must have an Insurable Interest in the person you wish to insure.
Insurable Interest means you either rely on that person for some means of financial support, or that you would suffer a financial loss as a result of that person's death.
For example, some grandchildren receive financial help from their grandparents to go to college.
Learn more about buying a life insurance policy on your grandpa.