I use Windows 7 32-bit. The portable version of calibre is working well for me with that operating system; it doesn't check during installation to see what version of Windows you are running. You can get it here:
https://calibre-ebook.com/download_portable
Note: Just because it's called the "portable" version doesn't mean you have to install it on a USB driver or any other external media. It will install fine on your computer's main hard drive. The portable version is updated on the website whenever the Windows version is; you'll be up-to-date.