Most term life insurance policies are guaranteed for the term (duration) for which you purchase the level premium. Keep in mind not all term life policies are guaranteed for the entire term of the policy.
For example, you can get a 20 year term life plan with a 10 or 20 year guarantee that the premiums will not increase for the first 10 years. Be sure to read your life insurance policy before accepting it so you can understand what the guarantee is, and how long your premiums are guaranteed to remain the same.
Permanent life insurance is lifetime coverage. You can get a permanent life insurance policy which is guaranteed to age 120. Keep in mind however, if the premium payment is not paid on time the guarantee provided by your policy could be at risk.