Be careful not to talk about songs from the olden days because people will know how old you are.
If you start talking about songs from a long time ago, everyone will know your age, so watch out.
この場合、次のような言い方ができますよ。
ーBe careful not to talk about songs from the olden days because people will know how old you are.
「年齢がバレるから懐メロの話はしない方がいいよ」
songs from the olden days で「懐メロ」
ーIf you start talking about songs from a long time ago, everyone will know your age, so watch out.
「懐メロの話をしたら年齢がバレるから気をつけてね」
songs from a long time ago で「懐メロ」を言うこともできます。
ご参考まで!