I often encounter URL's in Google that direct to an old URL.

For example, when I google on 'magento 2.3 installation composer', the first hit is http://devdocs.magento.com/guides/v2.0/install-gde/prereq/integrator_install_composer.html

Now, the 2.0 documentation is out of date for most intents and purposes, so it would be great if Google would point to the 2.2 documentation (and move to 2.3 after its release).

To achieve this you can add a canonical meta tag, so that Google knows that the 2.0 page isn't the canonical source any more. This also increases ranking as all the 'SEO juice' goes to the latest version, improving ranking if multiple version score for that page. Also it will prevent duplicate-content penalties by Google.