SmileNY

You look it. 並不是「你看那個」，而是「你看起來像那樣」的意思。句子中的 it 指的是年齡。You don't look it.意思是「看起來不像那樣(那個年齡)。」

想對年紀大的美國人說「你看起來還是很硬朗」，可以說：
You seem to be sharp as a tack. (tack n.圖釘)
You seem to be fit as a fiddle. (fiddle n.小提琴)

A: May I ask how old you are?
    能告訴我您幾歲了嗎？

B: I'm sixty-three.
    我63了。

A: Sixty-three? You don't look it.
    63？您看起來不像。

B: Everybody says so.
    大家都這麼說。

A: I'll bet. You seem to be sharp as a tack and fit as a fiddle.
    我也這麼想。您看起來挺硬朗的。

B: Thank you. I think I'm in the pink.
     謝謝。我覺得我很健康。