Tā / men / de / nián / líng / xiāng / chā / hěn / dà / péng / you / men / sī / xià / shuō / zhè / shì / lǎo / niú / shí / nèn / cǎo

他们的年龄相差很大，朋友们私下说这是老牛食嫩草。

There is a large age gap between them, so their friends privately call it an older person dating someone much younger.