Complex sentence: In 2010 a more modern analysis by Buckley et al showed the mean age of the skeletons was estimated at 12-14 years old.12 of the adults with assigned ages were over 50.
Split into simpler sentences: In 2010 a more modern analysis by Buckley "et al" estimated the mean age of the skeletons at 12-14 years old. Twelve of the adults with assigned ages were over 50.