[quote=Dead Cruiser]
Are the planes as old as the mortal world? Perhaps creatures that no longer live in the mortal world still cast their shadow in the Verdant plane.
[/quote]

Roughly. There is no definite age for any of the planes, as they are all technically sempiternal constructs of long-forgotten gods. They were likely constructed at different times, but that gap is infinitesimally small compared to the length of time that have actually been around. 

As for creatures casting their 'shadows' in the Verdance: the Planes aren't necessarily 'afterlives', per se. The Wraith Lands are a destination for souls by design, but the Verdance is a separate land created by some God to replicate Nature (or create his own) for some perverse reason.

Also the Mortal World is just another Plane.