What is meant by "Brahma Satya Jagat Mithya" of Advaita Vedanta?

According to Advaita Vedanta there really is no "right age" to get involved in spiritual pursuits.

Spirituality is not limited to offering daily prayers, reading religious books, going to temples, churches or mosques, undertaking pilgrimages to holy places, etc. Though these are good practices when compared to doing nothing they do not provide the much needed transformation in one's thinking and living so that one becomes a better human being.

According to Advaita Vedanta, Spirituality is to be practiced all the time and its goal is to reach the exalted form of human existence which is definitely possible and attainable. According to Advaita, Spirituality is nothing but being ethical, moral, honest, selfless, caring, loving, etc., bubbling with enthusiasm and radiating happiness all around.

At the young age, it is the responsibility of the parents and teachers to teach, cultivate and imbibe these values in the children. By growing up with human values and constantly accumulating the wisdom gained from various experiences in this world, automatically a time will come where one becomes curious and interested to know one's own true nature, the true Self which is the goal of the Advaita.

To answer your question about the "right age" to get involved in spiritual pursuits, Advaita does recognise it and suggests not the "right age" but the "right stage" in one’s life called Vanaprastha which is part of the Four Ashramas. One has to live the prior two stages Brahmacharya and Grihastha fully to the best of one's ability and all the time upholding the Dharma (righteousness and human values). Then as said before one would automatically understand the temporariness of the pleasures this world has to offer and become inclined to pursue higher human ideals.

Interestingly this is exactly what Socrates says, “The unexamined life is not worth living”, urging us to indulge in the worldly things so that we can have a deep comprehension of the world, clearly understand and realize the transient and momentary happiness they provide.

It was the same poverty-stricken Socrates while striding through the city’s busy central marketplace, looking at the mass of several things for sale, he would harrumph provocatively, “How many things I have no need of!“. That’s the sign of the wise who have developed Vairagya (dispassion).

Swami Vivekananda concurs by saying, “Fulfil your desire for power and everything else, and after you have fulfilled the desire, will come the time when you will know that they are all very little things; but until you have fulfilled this desire, until you have passed through that activity, it is impossible for you to come to the state of calmness, serenity, and self-surrender”.

Advaita has clearly laid out the goals which every human being needs to pursue in one's life and is called Chaturvidha Purusharthas, the four objects of human pursuit, Dharma (righteousness), Artha (wealth), Kama (desire) and Moksha (emancipation).

To make an effort to pursue these goals is called Sadhana and how exactly to focus and channelize the efforts is described in Sadhana Chatushtaya.

Do we need any external proof that we are a Conscious Entity, Consciousness, Awareness, Knowingness? I am using different words to mean the same thing.

According to Advaita, the goal is to realise and experience “being” a 100% Concentrating Entity, Pure Consciousness, Awareness. This is called Self-Realization. If one is sincere and earnest the goal is attainable and this is what I have explained in detail in my answer to How can I attain Self-Realization according to Ramana Maharshi?

Spirituality is nothing but science and it is the greatest antidote that is urgently required for all the today’s woes of the world as well as stress experienced by individuals.

Advaita makes us better human beings and adopted rightly, we could become great professionals too.

So the bottom line is to start reading Vedanta text books right away. Then understand and live what has been learnt.

See Also:

What’s the importance of Sadhana in spirituality?

What is Sadhana Chatushtaya?

What is the power of Concentration?

Are there any parallels between cognitive science and the philosophy of Advaita Vedanta?