If you have never installed Pages for Mac previously, it will not be in your Mac App Store listed under the Purchases tab, and thus, extinguishes any chance of getting the last compatible Pages version for your macOS installation. Apple does not provide user downloadable full Pages installers for past versions of it. The current version of Pages (v11.2) requires that the Mac is running macOS Big Sur or later.
To verify the first paragraph, launch the Mac App Store and sign in with the Apple ID used to previously install Pages v5 or later. Then, if on macOS High Sierra or earlier, press the option key while clicking the Purchase tab. If Pages is on this panel with an Update button, click that. You will receive a dialog stating that you need a newer version of macOS to install Pages. Acknowledge that dialog without clicking Cancel. A second dialog may appear offering to install the last compatible version of Pages for your existing operating system.