Why wouldn't they count to age 18? It would also seem that year 17 to 18 would be one of the priciest. So why exclude it?
Am I missing something?
Is 18 the age at which the person is qualified to work as an adult without restriction (hours, safety restrictions for children, etc)? And is it the age where people can legally sign documents (a lease, for instance) as an adult? I'm not sure, but maybe that's what they're getting at.
I don't care as long as the numbers for the past are calculated the same as current ones.