Short answer: Most group life contracts reduce the benefit at stated ages, and federal age discrimination rules allow it when the reduction is no greater than the higher cost of covering that age justifies, measured in age brackets of no more than 5 years. Cutting off coverage entirely because of age is not allowed.
The EEOC’s regulation on employee benefits says it is not uncommon for life coverage to stay level until a stated age, frequently 65, and then reduce. That does not violate the Age Discrimination in Employment Act, even if reductions start before 65, as long as each reduction is no greater than the increased cost for that employee’s age bracket, using brackets of no more than 5 years. A total denial of life insurance based on age is not justified, though coverage may end at separation from service.
The reduction schedule itself is in the certificate. It usually applies to voluntary life too, so for an older employee the voluntary rate rises by age band at the same time the benefit steps down. Revisit beneficiaries and any supplemental coverage when an employee approaches a reduction age.