They can live longer but most people only keep the layers for about 2 years, laying an egg everyday through 2 years wears them biologicaly down fast. So, it's not necessarily the life span but their productive live span that the 2 years is being referred too!
Most people that raise Cot's, raise them either for eggs or for meat....either one have a short life span by most standards, as compared to 'New World' quail. Wild 'new world' quail also have a horrific life span. Those kept in captivity can have life spans of 8 to 10 years.