The excerpt describes the swan as not aging at heart. It describes them as still being able to "wander where they will". While we know that everything ages physically, the author is showing how not everything about a person, or swan, must age. It's important here to eliminate options. The passage does not say anything about growing old, aging or changing. It says "hearts have not grown old." Any option that suggests the opposite should be eliminated. This means B-D should be eliminated.
