Upgrading from 32 bit to 64 bit is not possible with Windows. Also officially, you can not install a 64 bit Windows. Upgrading from a previous version may be possible. So officially, you can not install Windows 7, 8, 8.1 or 10. An iMac or MacBook introduced in late 2009 or later.A Mac Pro or MacBook Pro introduced in early 2008 or later.You can use a 64-bit version of Windows Vista or Windows 7 with any of these Mac computers: Any Intel-based Mac Pro, MacBook, or Mac mini.An iMac or MacBook Pro introduced in 2007 or later.You can use a 32-bit version of Windows 7 with any of these Mac computers: You cannot use a 64-bit version of Windows XP on any Mac computer. You can use a 32-bit version of Windows XP or Windows Vista with any Intel-based Mac computer.

On page 5 of Apple's Setting Up Boot Camp (copyright 2010), you can read the following. However, this type of firmware updating did not exist for any version of OS X officially supported for your Mac. Note: With recent releases of macOS, firmware update are include in the macOS installation software. See About EFI and SMC firmware updates for Intel-based Mac computers for available downloads. You can determine your current firmware version and apply updates by installing OS X.

This is why I think your Mac may not have the updated firmware to BIOS boot operating systems such as Windows. You Mac model was originally shipped with OS X 10.4.8 (Tiger). The press release Apple Introduces Boot Camp indicates Boot Camp was officially introduced with the release of OS X 10.5 (Leopard).

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