It depends on the insurance company. Each insurer that offers guaranteed issue policies has their own guidelines for age requirements to get guaranteed acceptance for a life insurance policy.
The age requirements usually vary from 45-75, 45-80, or even 45-85 years of age, to get guaranteed acceptance on life insurance.
Keep in mind, you may be able to buy a guaranteed issue policy from more than one insurance company, in case you need more life insurance protection.