How long will a 180 last? 6 Months. Maybe a year at the most. I got my lil guys around the beginning of July at about 1.5 inch. They are now about 8 inches and I'm sure will have NO trouble being well over a foot come Christmas time.
They grow VERY fast and definetly are NOT fun at all to move. They drop a LOT of scales.
It is best to have a long term plan well thought out before getting one. Mine barely lasted a month in a 75 gallon.