Synonyms for Decrepit (same or very similar meaning)
WordNet sense 1 (worn and broken down by hard use):
creaky, derelict, flea-bitten, woebegone, run-downWordNet sense 2 (affected by wear; damaged by long use):
wornWordNet sense 3 (lacking physical strength or vitality):
feeble, infirm, rickety, sapless, weak, weakly, debileWordNet sense 4 (physically weak):
frailFrom the ODE community, based on WordNetadd/edit