aging
modif.
declining, waning, failing, falling, sinking, mellowing, getting on, getting along, maturing, senescent, developing, fermenting, wasting away, wearing out, growing old, graying, lapsing, outworn, fading, crumbling, decaying, deteriorating, moldering, falling apart, doddering, one foot in the grave*, over the hill*, stale*.
*
Antonyms youthful, fresh*, vigorous.