just or only

[Rina]

May I ask what is the differenz between just and only?
Why do I say he's only 20 years old ?
Could I also say he's just 20 years old?

[Lucy]

Dear Rina,

When you say he's just 20, the meaning usually is that he had his birthday recently. So he's just 20 might mean he had his twentieth birthday last week. However, it would be more usual to say: he's just turned 20.

In the phrase: he's only 20, the underlying meaning is that he's still quite young. For example: he hasn't got a serious job with a pension scheme yet. That's okay, he's only 20. He's got time.

Lucy