"Show one's age" is a phrase that means someone or something is revealing its age through behavior, appearance, or attitude. There are several synonyms for this phrase, such as "unmask one's years," "betray one's age," "give one's vintage away," "exhibit one's seniority," "disclose the years," "display one's maturity," and "unveil the age." These phrases can be used in various contexts, such as when someone compliments an old book in a library and you say, "It's my grandfather's collection. It's showing its age," or when someone comments on how classic your car looks and you say, "Yeah, I know. It's revealing its vintage".