Gmail definitely does not enact this policy. Me and a friend managed to log into a shared gmail account recently we had from high school, to which no one logged in for more than a decade.
If costs got too much, they could easily take all very old emails and archive them - for example onto tape and cut down to one or even no online replicas.
Then add a button that says "Some emails and attachments older than 1 year are archived. Click here to retrieve them (takes 24 hours)"
It would be a security nightmare to let anyone else register and reuse an email address anyway. So the only benefit is saving a little disk space.
But disk space for highly compressible text that will probably never be accessed is super cheap.