Insurable interest means you may lose out financially if the insured person dies, or that you rely on the insured person for financial support.
There does exist insurable interest between parents and their children, spouses, siblings, relatives, and business partners, among others.
However, you may need the consent of your adult child, as well as his signature.
Having a life insurance policy at an early age will help ensure that your child has life insurance coverage in the future, even when your child's health deteriorates or when he gets involved with a hazardous occupation.
You should also consider whether you will remain the life insurance policy owner (where you have control over the policy, such as the decision of who to name as the beneficiary) or, since the child is already an adult, to transfer the ownership of the life insurance policy to your child.
Here's how you can request life insurance quotes for adult children.