Thread:TomodachiRoni/@comment-25691719-20161127082639

If this wasn't obvious already, let me explain. Any gem who endures more pain than their physical form can handle is poofed.

...So why has Steven never poofed?

Because he's part human. The bubbling ability is a last-minute resort that takes place when the sword and shield are not enough to protect him. He now has a newer ability that allows his bubbles to look like morningstars, allowing him to prop himself up against other objects like walls.

Steven would not be able to poof due to his 50% human genes. Sure his feelings about how old he is can change his age, but he can never, ever poof. He's flesh and bone in there with a gem smack dab in the middle. It's possible that Rose knew this and decided to help him with the bubbling ability. 