Since he is related to you, being your uncle, there is an insurable interest. However, you will need his permission and signature in order to buy the life insurance on him, and he may need to answer some health questions, and maybe take a physical for the life insurance.
However, there are some insurers that may offer no exam life insurance plans, such as, Globe Life, Colonial Penn, AARP/NewYork Life, Mutual of Omaha, Garden State Life, and Fidelity Life, among others.
There is a life insurance broker online that has a network of over 70 highly-rated insurance companies and offers life insurance quote comparisons form insurers that do and do not require medical examinations.
Here's how you can learn more about how to buy a term life insurance policy with no health exam required. You can request a free quote online and apply for coverage.