HER parents say her body is trapped in a time warp. Her doctor believes she might hold the secrets to the fountain of youth.

At the age of 17, Brooke Greenburg still looks like she did as a toddler. She cannot walk or talk, still has milk teeth and weighs only seven kilograms.

''Without being sensational, I'd say this is an opportunity for us to answer the question 'why we're mortal' or at least to test it,'' Dr Richard Walker, of the University of South Florida, said after preparing a paper on her condition. ''If we're wrong, we can discard it. But if we're right, we've got the golden ring.''

Brooke's father Howard says his daughter ''stopped ageing'' after her fifth birthday.

''She did have some development changes from one to five,'' he tells Channel Seven's program Sunday Night this evening. ''But from 5½ to 17, you can't tell the difference at all.''