Hi Jon,
What this message means is that somewhere in you are referencing a component which works in 6.3 but may no longer work in 6.5.
In this specific instance, it looks like your contentpage component overrides wcm/foundation/components/page, which is deprecated in 6.5. The new component to override is wcm/foundation/components/basicpage/v1/basicpage.
I am actually also doing a 6.3 -> 6.5 migration at the moment and I highly recommend you migrate towards AEM Core Components which implements many common components (including a Page component) using the latest best practices and a number of great features! Much easier than re-inventing the wheel, and it's backed by Adobe so you don't have to worry about compatibility issues or support