[误] My grandpa is running for seventy-five.
[正] My grandpa is getting on for seventy-five.
注：run for 有“竞赛，竞选”之意，如：run for Congress(竞选国会议员)，run for the presidency(竞选总
统)等。而 get on for 才表示“接近”，它通常用进行时态，后面一般跟年龄或者时间，如：It's getting on for midnight(快到半夜了)等。
(1). push thirty[forty,etc.]已经快到三[四...]十岁了：
She would like you to think so, but she's pushing thirty.
You wouldn't think so to look at him, but he's pushing 40.
(2). get on for[towards]快到(某时间)，快(多少岁)：
It's getting on for nine o'clock.
He must be getting on for forty now.
Here you are getting on toward thirty.
1) I'm twenty.(常用)
2) I'm twenty years old.(常用)
3) I'm twenty-year-old.(不常用)
4) I'm twenty years of age.(书面)
5) I'm aged twenty (years).(书面)
6) My age is twenty (years).(不常用)
7) I come into the age of twenty.(不常用)
8) I'm in my teens.(不常用)
in one's early teens(不常用)
not yet out of one's teens(不常用)