Congratulations on turning forty years old!
祝贺你满四十岁！

N-COUNT. 转折点;转机. A turning point is a time at which an important change takes place which affects the future of a person or thing.
VERB. 扭;拧;搓;捻. If you twist something, you turn it to make a spiral shape, for example by turning the two ends of it in opposite directions.

The timing of the gun was precisely synchronized with the turning of the plane’s propeller.

风门的调速与飞机螺旋桨的转动精确同步。

Look for the turning, for something or nothing.

看看那个转弯处，是为了我们吗?

※Woe is me. Me thinks I'm turning into a god.——Vespasian, Roman emperor 吾即苦难。我想，我将转为神。罗马皇帝 斯佩西安