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).

Macbook os x 2007