Why is the Grim Reaper so immature and childish?

[C.S.]

I’ve noticed a recurring theme in some of the reviews about the Reaper’s maturity level and overall vibe: that he’s overly whimsical and not stoic enough for someone called the prince of the underworld. Here are my reasons for writing him the way I did.

What I’ve learned about those who have truly suffered loss and kept living is that they don’t become distant or detached. They actually grow more joyful. They develop a deeper appreciation for the smaller things in life...the sound of singing sand, the feel of the wind, the drip of cheese from a greasy burger. Once death has been encountered, everything that follows becomes a gift.

This was the Reaper.

He is deeply sorrowful and pained by his existence and mission, but that pain only makes him appreciate life all the more. It gives him a sense of playfulness and recklessness.
Yes, Sonny’s experience with him does seem to make the Reaper feel younger, but that is only part of it. The Reaper is who he is because the fragility of life is meant to be enjoyed. To live that way produces a spirit that transcends cold, marble stoicism.