My information comes from my personal experience and research, much of it on this site and Loaches Online. In most cases I have kept the original links to the information and/or downloaded the publication. Unfortunately, some links expire and the original information cannot be retreived.
Marge measured 11.5 inches when alive as reported several times by her owner Emma Turner on Loaches Online (links still live), though when measured after death in April 2020 she measured the full 12 inches. I expect fish swell up with water when the osmoregulation fails. Marge's age was not known as the retailer did not ask the previous owner.
When I bought my Loaches there was no internet info and retailer information was that the lifespan was 10 years and a 3 foot tank was required. My own largest fish which I purchased in a group of six in Jan 1995 and have kept in a 6' x 18" x 18" aquarium since that time is also 11.5 inches. I'll post a picture below.
I believe that captive Clown Loaches rarely exceed this size and they rarely reach this age.
I know that larger fish have been taken from the wild and 14" examples have been shown on here.
Someone from Jakarta who exports fish once said on here that it has been illegal for Clown Loaches over 4 inches to be exported since at least 2006, but I have seen that the law is frequently broken as demand and rewards are high. The law is there to protect breeding stocks and ensure the supply of young fish for the trade. It is far cheaper to catch wild yearlings for the trade than to breed them using hormones.
I know that owners who have obtained very large Clown Loaches from the wild have found that they do not acclimatise well to captivity and nearly all have died within a year.
I do not think that 14" is a regular size in the wild as researchers have interviewed fishermen in the region who stated that 8 to 10 inches is a more usual size.
Scientist Marc Legendre also states in his scientific paper that he caught 3,000 fish in Sumatra and only one reached 12 inches.
Much of my information has been discussed with, shared with or obtained from JD, a member on this forum who has coordinated discussions of this type.