In several ways, Beloved is a baby/child. This is demostrated in her difficulty with walking at first, in the fact that she was unable to speak fluently at the beginning, and the spontaneous loss of a tooth. After all, the story reveals that Beloved is indeed Sethe's deceased, infant daughter.
In other obvious ways, Beloved is a woman, of the age she would have been, had she survived her injury. She is fully developed physically, and is at her peak sexually, as evidenced by her relationship with Paul D.
Not only is Beloved an infant and a woman, she is also, some might say, a demon. Others might call her a restless spirit. Nevertheless she is supernatural &/or paranormal in existence, as evidienced by her ability to "move" Paul D.
I hope this is helpful.