We currently have 12 koi. The 5 small ones we got last year. 6 of the 7 larger ones we got about 10 years ago. They were about 2-3 inches in length at the time. One of the spotted ones was in the pond when we bought the house in 2003, and he was probably about 5 years old then. 3 of the original 4 from 2003 died or 'ran away'. 1 was struck by a limb from our neighbors large oak tree during a storm, 1 got sick and was put down which required us to quarantine the others for a few days, and the other just mysteriously disappeared (our guess, either a heron, hawk, or raccoon).
The small ones don't have names, but some of the larger ones do, sort-of. Dinsdale (from 2003) survives Doug and the other 2. Then there's Whitey and Big Fatty, along some subset of Greg, Peter, Bobby, Marsha, Jan, and Cindy. You can probably guess Whitey and Big Fatty from the pics. As to the Brady kids, your guess is as good as mine.
I built them a 'garage' out of a large piece of slate, using bricks for pillars to park their fishy butts in. And while they a much bigger now, they still try to cram themselves in there when they want to go into stealth mode. As a size comparison, you can see a full size brick that makes up part of the one pillar in the pic where there are a couple other bricks on the stone edging. I think a couple of them are bigger than the neighbors cats that come by. Not the best pics, but you can make out the brick just above Dinsdale's head in the top right pic. We leave the waterfall (bottom right) running constantly except for a few hours when they're fed.