I will certainly tell you, Socrates, what my own experience of it is. I and a few other people of my own age are in the habit of frequently meeting together, true to the old proverb. On these occasions, most of us give way to lamentations, and regret the pleasures of youth, and call up the memory of amours and drinking parties and banquets and similar proceedings. - The Republic of Plato
What's the meaning of true to the old proverb? I couldn't find the old proverb.