Yeah but how old, and how many used up was the laptop?
Is this a correct English sentence?
Assuming he was asking as to the 'wear and tear' of the laptop, the "Many" and "Used up" in the same sentence make it redundant.
Properly formed:
"Yeah but how old
The "up" being present in the sentence becomes questionable, because "used up" tends to mean depleted, as in you drank the entire glass of water. There's no more left. Using this term on something like a laptop... while probably not the best way to phrase it still works... kind of. This is what is known as English "Slang." People understand what you're saying... it's just not exactly proper. However, if you ever visit New Orleans you'll see how prevalent and common place slang is.
English is a stupid language, so try not to understand it too much.
According to englishery rules, this sentence is grammatically sound:
Wouldn't the sentence 'I want to put a hyphen between the words Fish and And and And and Chips in my Fish-And-Chips sign' have been clearer if quotation marks had been placed before Fish, and between Fish and and, and and and And, and And and and, and and and And, and And and and, and and and Chips, as well as after Chips?
However, I think Matt_C may have just left "many" in there as the remnants from another line of thought, but didn't backspace enough.