才 + Number (only — a small amount)

Only that much?

You've met only then / not until才cái for lateness. It has a second job.
Before a number, only then / not until才cái stresses the amount is smaller than expected — "only, just."
"You're only twenty?" — you你nǐonly then / not until才cái二十岁èr shí suì?

Practice

你才二十岁? means …

you你nǐonly才cáitwenty二十岁èr shí suì？

only then / not until才cái二十岁èr shí suì = "only twenty" — surprise that it's so little.

Practice

Complete: 这家店 ____ 开业一个星期。(This shop has only been open a week.)

Practice

Before a number, 才 stresses that the amount is large.

Practice

Build: “They've only known each other three months!”

Before a time → "late" (十一点shí yì diǎnonly then / not until才cáito / arrive到dàohome家jiā).
Before a number → "only that much" (only then / not until才cái二十岁èr shí suì).
Both share the feeling "less than expected."

Explore

才 + number shrinks the amount: only five, merely ten kuai — and no final 了.

Key idea

only then / not until才cái + Number + Measure Word + Noun — only (a small amount)
Surprise that the quantity is so small
Same only then / not until才cái as "lateness" — both mean "less than expected"

Read the full reference: HSK 3 grammar — Adverbs.