What size shirts does a 14 year old wear?

I am 13 girl ( almost 14 ) and can fit anywhere from 8-14 in girls and nothing over a size 4 in juniors but it depends on the brand. For example in Justice clothes I can fit a 10 in tops but clothes from Wal-Mart I wear a 14 in tops. But everyone has a different body shape but my opinion is that a average 14 year old girl should not be over a size 16 in girls or 6 in juniors