A tart temper never mellows with age, and a sharp tongue is the only edged tool that grows keener with constant use.

Irving contrasts two kinds of “sharpness”: the sourness of a bad temper and the cutting wit of a cruel tongue. Both are presented as habits that do not improve on their own with time; age does not automatically sweeten character. The second clause sharpens the warning by using a tool metaphor: most edged tools dull with use, but a biting tongue becomes more effective the more it is exercised, as practice makes one quicker and more confident in sarcasm or insult. The implication is moral and practical: unchecked irritability and verbal cruelty are self-reinforcing, so civility and self-command must be cultivated deliberately rather than expected to arrive with maturity.