10 - 20 years = with hibernation, super well taken care, perfect water quality, etc. etc
5 years = our tropical weather, good water quality, etc. etc,
I remember we've ask my Japanese Ranchu Sensai before, He told us in Japan, with normal care, fish will last 8-10 years. He says don't expect our fish live more than 6 years in Malaysia.
Derrick's answer is almost spot on. *respect*
Cheers
