I went to Beijing by train the first time When I was 28.

问题描述:

I went to Beijing by train the first time When I was 28.
选at or for
I went to Beijing by train ————the first time When I was 28.

for the first time 首次;第一次
at the first time 第一时间
所以
选for
就是说,我第一次乘火车去北京是28岁得时候谢谢啊呵呵,不客气