I think you are talking about the girl who has progeria. People with this disease tend to be smaller than average and age normally until they are infants but then seem to stop ageing. However in lots of ways they are undergoing accelerated ageing. They have a loss of hair, they develop wrinkles, they loose body fat and muscle and have joint problems, just like the elderly. This disease is caused by a mutation in a gene that is important for maintaining the structure of our cells nucleus. for more information see http://hayleyspage.com/.
is this the person you were talking about? hope this helps.