Juvenile or not they still need a suitable environment to develop in and being in a crowded tank is not going to give that to them.
Would you keep a baby in a small area because you cannot provide for it...simple answer NO, why should fish be different? Answer again, WE treat them differently because they cannot answer back and tell us when something is wrong.
You make a commitment to care for your fish to adulthood once you purchase them...you cannot just drop them because they have got to large, imagine doing that to a baby, sorry, it got too big, I dont want it....
Never assume that something might happen, ie getting a bigger tank, I mentioned in another post, about purchasing a glass panel for a 500g fish tank I was planning on building for a massive cichlid colony...the glass was a steal and I simply could not turn it down. Well, 2 years later and the pane is still in my garage waiting for the tank to be built...
Point being, we can all say we want a bigger tank, I have a 29g saltwater tank running for not even 6 months yet!, already am thinking about a larger one...with the extra tank size comes the added cost of upgrading equipment as well...what turns out to be a buy the tank suddenly gets into well I need X,Y,Z as A,B,C I have for my tank now will not work.
Keep a close eye on the water parameters and signs of illness etc and yes it could potentially work, with the general knowledge of not only this community but other forums as well, in hindsight it will likely cause more problems than simply stocking the tank appropriate for the size NOW.
As Byron mentioned, there are signs effecting the fish which you cannot observe directly until it is too late sometimes, that is why we need to provide an environment suitable for the care of the fish regardless of what state of development they are at.
Fish aggression is not always visible to us, you might observe it but 90% of the time you will not.
My male Auratus
when I got it was a juvenile, that didnt stop it having a chase with my fully grown Demansoni Male when it went into the tank... the Demansoni was number 1 in the tank pecking order by a long way...along comes the Auratus
at under half it's size and bam...pecking order changed. To the day I sold them, it was still number 1 but being harassed for top spot by it's own son!
Fish generally calm down when we are in the room as A) they associate us with feeding time B) our larger presence can spook them....now when we leave things happen we may not see.
Am not saying that this tank will NOT work period but will just need careful monitoring to make sure nothing happens, and to avoid injury, illness or deaths. If your fish dies, you wasted your money...another reason we provide a suitable environment for them to sustainably live...I hate to use it but Africa is a prime example of this in humans, many many deaths occur because basic humanitarian qualities we associate with every single day are not available to them, clean water...same example can be used for us maltreating fish and not providing for them.
While I respect your comments and hope that you will respect mine, asking a question on a public forum will provide varied responses, some of which will be good and some will be bad...we chose to join here to share our knowledge be it personal or scientifically proven to other members. Being obviously a fish forum, we are here to provide care and assistance in bringing up our chosen species.
My apology for this long post...