了
le
Change of state with "le"
Sentence-final 了 reports that things are now different from before.
New Situation + 了
How it works
我25岁了 — I'm 25 now, meaning I've just turned 25. Without 了 it's a bare fact; with it, it's news.
It works with adjectives (天黑了), nouns (春天了) and verbs (他来了).
This is the same 了 as in 下雨了 at HSK 1, seen across a wider range of sentence types.
Examples
wǒ èr shí wǔ suì le
我二十五岁了。
I've turned twenty-five.
tiān hēi le
天黑了。
It's got dark.
tā huì shuō zhōng wén le
他会说中文了。
He can speak Chinese now.