I reached that certain age and fell in love.

我到了既定年龄却陷入爱河。

youdao

Human brains come equipped with certain quantitative instincts that are refined with age, but these instincts are very limited.

随着年龄的增长，人类的大脑具有了一定的数量本能，但这种本能是非常有限的。

youdao

Some scholars conclude that a government with finite resources should simply stop paying for medical care that sustains life beyond a certain age—say 83 or so.

一些学者得出结论，资源有限的政府应该停止为超过一定年龄的人（比如83岁左右）支付医疗费用。

youdao

But almost one in five (19%) said that being middle age is a state of mind, rather than something that begins at a certain age.

BBC: Middle age begins at 55 years, survey suggests

Second step: They can sign a contract--symbolic, not binding--stipulating that, by a certain age (provided the business is not in financial distress) that they will move on and let the next generation take its lumps.

FORBES: Head Coach

Newt Gingrich reminds me of one of those small, ugly dogs that women of a certain age make a tremendous fuss over.

BBC: Newt Gingrich and his campaign legacy