I haven't commented in a long time, but the reporting on this subject is heavily biased to support the pre-determined conclusion that the manuscript predates Mohammed (pbuh). The Daily Mail is guilty of this (shock! horror!) and so is the summary with its strategic "typo".
From the Mail article, Carbon dating places the manuscript between 568 and 645AD, while Mohammed is thought to have lived between 570 and 632AD. Most intelligent persons would take a quick glance at those dates and be able to dismiss the headlines outright. The range on the dating is nowhere near precise enough to make such a bold statement which is obviously meant to be inflammatory.
Also, as others have rightly stated, the dating is for the parchment, not the ink itself. It is perfectly possible for the parchment to have been produced and not been used for a length of time. Writing paraphernalia was extremely precious at that time; they may have been saved for something important.
Finally, while it is correct that the FULL Quran was not compiled in written form until after the prophet's death, and was primarily stored in memory of the followers, that does not preclude writing completely! The discovered script contains only a couple of chapters, and is not a complete version.
tl;dr: inaccurate and sensationalist headline and reporting on results which may actually point to the opposite.