Final answer:
Max Griffin is the Stonekeeper who assists Emily before his death. He appears young but is about fifty years old and has a redemptive arc in the story.
Step-by-step explanation:
The character in question who appears young but is actually around fifty years old, ultimately helps Emily, and dies is Max Griffin. Max Griffin is a Stonekeeper who initially joins the elves but has a change of heart and assists Emily in her quest. Despite his initial allegiance to the antagonists, his complex backstory and ultimate redemption make him a memorable character in the series.