The installation date of your computer's BIOS is a good indication of when it was manufactured, as this software is installed when the computer is readied for use. To check the BIOS installation date in Windows 8, press "Win-R" to open the Run dialog window, type "msinfo32" (without quotes), and then press "Enter" to see your computer's system information with all the details of your model and installed components. Look for "BIOS Version/Date" to see what version of BIOS software you're running, as well as when it was installed. Note that this will only indicate the manufacture date if you haven't updated the BIOS from the original version that came preinstalled on your system.
Your computer's operating system was installed after the machine was assembled, and this date can serve as a good indication of original manufacture. To find your operating system installation date, press "Win-R," type "cmd" (without quotes), click "OK" to open the Command Prompt window, and then type "systeminfo" (without quotes) on the command prompt to see a list of all information regarding your system, including the operating system's original install date. Note that this date is only accurate as a manufacturing date if you haven't reformatted your system and reinstalled the operating system at any time since purchase.