You say the webview is out of date, but then you ask:
Add a link at the start of the game when it’s not working to redirect to the android update page?
The message shown when the webview is out of date already does show a link for the user to install the right update. So are you sure you are seeing this message? Are you sure it's to do with the webview version and not something else?
FYI the update should be there if the device has auto-updated from the Google Play store any time in the past ~3 years. It's hard to imagine why this would not have been the case. If the devices are failing to update due to running out of storage, then there won't be room to bundle a browser engine with it either, so that seems like a non-starter - but it's not clear that's the reason the devices are out of date. If they really are using very old versions of the Android WebView, I'm keen to find out the reasons behind this, and would be grateful if you could shed some light on that.
We have asked Google to add a minimum required WebView version for Android apps, but so far there doesn't appear to have been any progress on that. More customers asking in that issue might help.