The entire study is founded on the age of the specimen. That age was determined to a literally unbelievable level of precision (+/- 31.025 days for a 50,000 year old corpse of a species that went extinct 40,000 years ago) by assuming that neanderthal growth rates were effectively identical to homo sapien growth rates - so enabling them to determine its age by markers based on homo sapien growth rates. They then use this assumption to show that the growth rate of neanderthals were not, in fact, identical to homo sapiens. This seemingly contradicts the assumption they used to determine the specimen's age, which in turn would effectively nullify the entire paper since it thus negates any attempt at such a precise measurement of age.