Can we have any nation or society building without caste system ?
Answer is a big No

In fact all developed nations are based on that only. The challenge is the rigidity and unfortunately there are reasons for it and similar mindset is there in other aspects also.

For a society to start forming the first important pillar is knowledge and wisdom.
This wisdom then converts into something which were traded with others, thus the seeding of commerce as second pillar. The third pillar was necessitated when the society grew and thus was the need for structure, combined security and rule based activities. Thus came in governance. Both pillars are born out of the first pillar.

All these pillars require support staffs. Just like we have in present day organizations.

This support staff is the fourth pillar.

No society or nation can be build without these four.

Now how old is this in the context of our history ?

Even all puranas, Ramayana, Mahabharata have reference to these. It means our society was structured from almost time immemorial.

Once a society is structured then the knowledge gathering becomes structured. So there will be local temples which acted both as Charitable institute and also primary education centres. Then there were gurukools for different streams. And there after later advance studies were through our ancient universities starting from Taxila and biggest was Nalanda. We had more than 70 universities by the time of the start of the attacks by Islam invaders.

I hope the 4 pillars or streams are identified. They are similar to present day streams of career.

Knowledge and wisdom - this stream was called Brahmin

Trade and commerce - Vaisya

Governance and security- Kshatriya

Support services - Shudra

All are indispensable and important. But most important is knowledge and wisdom. If that is eliminated then society decay starts, which hapoened when all of 70+ universities were destroyed. Brahmins were killed and rendered jobless.

When structured way of knowledge dessimination was destroyed then the knowledge was passed on through family. It's just like the dynasty of kings, politicians, bollywood actors, etc. This is a different subject - how bharat became weak.

But sticking to subject, call the caste system by any name, but those are the key pillars of any society or nation building