老太婆 can be neutral or derogatory depending on context. Used descriptively it just means 'old woman,' but when used to criticize someone it becomes insulting. The polite terms are
老太太 (lǎotàitai) or
老奶奶 (lǎonǎinai). When a man calls his wife
老太婆, it is an affectionate/humorous term.