1.at the age of+某人岁数
e.g:At the age of 18,LiMing learned how to drive cars.
在李明18岁时,他学会了如何开车.
2.in one's+数字基数词复数
e.g:in his twenties在他20岁的时候
in Wanghua's sixteens在王华16岁的时候