(2) Where there is proof of the true age of the life insured and such age is greater than the age on which the policy is based, the company may vary the sum insured by and the bonuses, if any, allotted to the policy so that, as varied, they bear the same proportion to the sum insured by, and the bonuses, if any, allotted to the policy before variation as the amount of the premiums which have become payable under the policy as issued bears to the amount of the premiums which would have become payable if the policy had been based on the true age.