Most term policies are Level Term, with premiums that remain level for the duration of the policy term - either 10, 15, 20, 25 or 30 years.
However, if you have a term to 70, or term to 90 policy, the premiums may remain level for the first 20 or 30 years, then increase each year thereafter until you reach the age 70 (or 90).
Also, if you choose to renew your term life policy, your renewal premium will be based on your age at the time you renew your coverage for an additional term.
To learn more, read this article: Can Term Life Insurance Premiums Increase?