I have three shubunkin. Ernest must be at least 5 years old, but he's only 6 inches from head to tail since my dad kept him in a 30 litre tank with about 5 other goldfish.
The other two are around 3-4 inches and don't seem to be growing much as I only do water changes once a week. At the moment, everyone lives in an over-filtered 200 litre tank; however, they will be moving into a 450 litre tank at the end of the month.
Eventually, when our house gets renovated, they will be going into a planted, 1000 litre pond built into the deck.