How to incorporate coverage amount limitation for an employee entered coverage based on age

There is a requirement for the policy's payout amount once you reach a certain age. For life insurance policies at age 65, the benefit is reduced to 65% of the original amount. If you bought a $15,000 policy, the payout to your beneficiaries would drop to $9,750 after your 65th birthday ($15,000 x 65%).
After age 70, the benefit is further reduced to 50% of the original amount. ie, the $15,000 policy would be reduced again to $7,500 after 70th birthday ($15,000 x 50%). How can this be achieved. Any possible work around for this?

Note: The policy coverage amount is user entered.