It would appear you do not need to be retired to take the ME non-military pension deduction. The only mention of an age restriction is here (extracted below) in the ME form 1S instructions.
"... except that pick-up contributions received from the Maine Public Employees Retirement System (“MainePERS”) allowed to be deducted on Form 1040ME, Schedule 1S, line 7 and pension income from 457(b) plans received prior to age 55 that is not part of a series of equal periodic payments made over the life of the recipient and the recipient’s designated beneficiary, if applicable, may not be included in the deductible pension amount."