Translation of "Downhill" in Japanese

But this is when my journey started to go downhill.

私は転落を始めていました

For a girl, after 30, it's downhill all the way.

女は３０を過ぎてからはずっと下り坂だ。

The weather is supposed to go downhill starting this afternoon.

午後から天気は下り坂になります。

The path that water would take on its quest to flow downhill,

水が下に向かって流れると思われる

- After the rain, fair weather.
- There is a downhill after every uphill.

雨の後は良い日が来る。