That really depends on your age and health; as well as, the insurance company.
Usually, the longest term for term life coverage is 30 years.
However, there may be some insurers that offer up to 40 years of term life insurance to younger adults.
Usually 30 year term life is level premiums and level coverage amount of the 30 year term.
However, some plans offer level premiums for 20 years, but term life coverage up to a certain age; for instance, age 70.
With these plans, you pay a level premium the first 20 years you are insured, then your premium steadily increases each year until you reach the maximum age covered by the policy.
Learn more about term life insurance to age 70.