A health insurance policy is generally issued for a period of 1 year, at the end of which you need to renew your policy. Some companies, however, also offer policies for a duration of 2 years. For some products, the renewal of the policy will be at the discretion of the insurance company and would depend on a review of health conditions and a possible medical examination.
However, in other cases, a renewal is guaranteed up to the maximum age of coverage under the product, as long as the required premium is paid. For e.g. if you purchase a health insurance policy at the age of 35 and the product provides a health cover up to a maximum age of 70, then you will be assured of a health insurance cover to age 70 years on payment of applicable premiums every year.