岁月是把杀猪刀
[suì yuè shì bă shā zhū dāo]
The idiom '岁月是把杀猪刀' metaphorically means that time (or aging) is like a butcher knife. It reflects the reality that just as a knife can make visible and permanent marks on meat, similarly the passage of time leaves traces on humans, often referring to the impact of time on one's appearance or youth. Time mercilessly 'cuts' away the vitality and beauty of our younger years.