By 2014, that milestone (里程碑) had shifted to age 29.
2019年6月四级真题（第一套）阅读 Section B
英语六级真题
It is a milestone in human progress.
出自-2013年6月阅读原文
It was a huge milestone in the development of smartphones, which are now owned by a majority of American adults and are increasingly common across the globe.
2018年12月六级真题（第一套）阅读 Section C
Some experts even consider lying a developmental milestone, like crawling and walking, because it requires sophisticated planning, attention and the ability to see a situation from someone else5 s perspective to manipulate them.
2019年12月六级真题（第一套）阅读 Section C
柯林斯高阶英汉双解学习词典释义
N-COUNT
里程碑;重大事件;重要阶段
A milestone is an important event in the history or development of something or someone.