I am pretty lost with the story. So first they say only every few decades 20 something people can even enter that area and they only send young people. But than they can all just call their masters? And they can easily enter? So how is there any treasure left? Why did the Masters not enter from the beginning and just loot the place?

I think you misunderstood it. I know sometimes subtitles can be very messy.
There is no age limit in this Realm. It was in Nandu Capital. Remember where our MC got the demon seed. This Realm has cultivation limit.
As far as I have understood the subtitles and storyline, they never said that only younger generations can enter in this area of Demonic Realm.
They said that each person sent in different area of demonic realm w.r.t their cultivation level.
The higher the level, the deeper you land in this Demonic Realm.
Only Divine Level Martial Realm (Wuzong), Martial Venerable, Martial King and Martial Martial Sovereign Realm people can enter in this Realm. After finding out about this place, many Martial Sovereign who were stuck in their Realm entered and successfully break through the Martial Emperor Realm and creat 100 dynasties. Once upon a time, there was a Martial Emperor who tried to enter in this realm but got killed due to Realm restrictions. Our Mc said, there are some realm which has some restrictions on cultivation cuz’ high cultivation level can destroy the Realm.
I hope I have cleared the misunderstanding.
Edit: I have corrected some typing mistakes.

There is a limit. In novel, it was 1000 people when properly divided by strength like it was planned. Martial King amounts for 10s of Martial Venerables. Basically, in previous entrances they measured how much and how strong.

Second limit is how far the space tunnel was restored. This is why that opening 18 years ago limited so much. Qin Chens father is too strong even when dumbing down his power, but due to his strength he could survive the space tunnel limitations. But, once too much people or strength passes through, tunnel colapses

And it is not deeper with strength. Everyone is randomly thrown at outskirts. It is just that weaker would have trouble surviving in central area, while strong have zero benefit in outskirts. This is why everyones movement is like it is. Weaker than Venerables would have zero survival chance and zero benefit, making it pointless. And there is only one Emperor in whole continent (old lady) which would be too strong for the tunnel and too weak to survive the collapse. So, weaker are limited by environment, stronger by the tunnel.

Thanks for the info🙏.

Major plot hole. I was thinking the same thing.

I have answered this in my comment. You can check out my reply to @Collet3 to clear your confusion.

My comment with the 20 something was not referencing the age, but the amount of people. I am sure they said something along the lines of: Normally we send like 20 people but somehow a while ago someone already send 6 people in so now we can only send 14. (numbers might be wrong but essencialy thats what the subs said).

But the subs might have simply explained it wrong as you said.

This is just animation taking shortcut, like all animations. In novel it was 1000 people, not 20. Or look at "Against sky supreme"... at the exact point where it is, in novel entred the realm 5000 people, in animation... 40-50?

It would simply mean too complex animation work for small time frame

Agree! I was also always at a loss whenever they said 3000 5000 people but only people they animate are 40 50 or may be even less than that.

Yeah it is.
In Chinese 百分之 means percent. But subtitles were also pretty off.
It is said that portal can only be opened once after some decades (I don’t remember the exact years, may be it was a century or something) but the total quota has been reduced cuz’ some one has already entered in this realm in the same year which is why 20% people will not be able to enter in this realm. People from Lower dynasties started to rush as Upper and Middle dynasties will be able to enter and they will be left behind. Limited amount of quota has been divided in Upper, Middle and Lower dynasties. Btw Lower Dynasties can only send Wuzong and Martial Venerable Realm practitioners, Middle Dynasties can send from Wuzong to Martial King Realm practitioners and Upper Dynasties can send from Wuzong to Martial Sovereign Realm practitioners.

In the subtitles they did write 20 percent not 20 something, at least that is what I remember.

I was also at a loss when @Collab3 said that but then I thought may be he has watched it somewhere else and no matter where u watch, there are always many mistakes in subtitles. So that’s why I said that.
Edit: Plus I also didn’t remember the exact dialogue and episode, so I didn’t want to engage in unnecessary discussion. I hope I have answered your question.

it will take another 10 episodes to decide who gets the treasures
but as we all know most likely mc will get all of it it in the end LOL!!!

Nope, only one matters... the jade plate

XD

Um tap tap they aren't just 6 ppl in the room