Usage of the words: those and these and them

[Richard]

That would be about 100 billion stars. But of course, you couldn't even count them in your lifetime, could you?

Is this sentence wrong?
You couldn't even count those in your lifetime, could you?

The sentence I have just mentioned sounds odd to me but I just want to know that whether it's correct or not.
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The limits of my language are the limits of my universe.
Ludwig Wittgenstein

[Mister Micawber]

'Them' is fine, and it sounds better than 'those' to me.
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Native English teacher at Mister Micawber's