(1) The insurer may in any group life insurance contract provide that it is not liable, or is liable only in a reduced amount, for losses resulting:

(a) From war or any act of war, declared or undeclared, or of service in the military, naval or air forces or in civilian forces auxiliary thereto, or from any cause while a member of any such military, naval or air forces, of any country at war, declared or undeclared.

(b) From aviation under conditions specified in the policy.

(2) The insurer may in any such contract provide that any amount of insurance in excess of one thousand dollars on an individual life may be reduced to one thousand dollars or to any greater amount upon attainment of any age not less than age sixty-five or upon the anniversary of the policy nearest attainment of such age.