"三十岁左右" 用英语可以说 "around thirty"。
"Around" 意思是 "在...周围"，"thirty" 是 "三十"的意思。所以 "around thirty" 就是 "三十岁左右"的意思。
例句：
He's around thirty years old. 他大约三十岁。
She's in her early thirties. 她三十岁左右。
I think he's around thirty. 我认为他三十岁左右。
不同的说法还有：
in one's thirties (年龄在三十岁左右)
in the early/late thirties (年龄在三十岁初/晚)
提醒：在英语中不能说"三十岁“，只能说”thirty years old"