Could naval treaties discount the tonnage of ageing battleships?

Could ageing battleships count for progressively less treaty tonnage instead of being written off at a fixed date?

The proposal could preserve useful ships, but a fixed age is judged easier to negotiate than allowances for each ship's individual condition.

Dan proposes reducing the treaty tonnage attributed to a ship as it ages, allowing useful older battleships to remain without consuming their original allowance. His illustrative figures fall to 80 percent at fifteen years and 60 percent at twenty years. Alex Clarke replies that individual ships differed too much for such adjustments to be agreed readily. A fixed retirement age was easier to negotiate, even though age and remaining usefulness were imperfectly matched.