What is the age of Rig Veda?

Many scholars say the age at which Rig Veda, the earliest Veda, was composed is 1500 –  1200 BCE.

Rig veda II.15.6 says

सोदञ्चं सिन्धुमरिणान महित्वा वज्रेणान उषसः सं पिपेष | अजवसो जविनीभिर्विव्र्श्चन सो... ||

sodañcaṃ sindhumariṇān mahitvā vajreṇāna uṣasaḥ saṃ pipeṣa | ajavaso javinībhirvivṛścan so... ||

With mighty power he made the Sindhu (stream) flow upward, crushed with his thunderbolt the car of Uṣas, Rending her slow steeds with his rapid coursers. These things did Indra in the Soma's rapture.

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The word Udīcī (उदीची) has different meanings.

One is Upwards and another is Northwards

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Rig Veda I.164.45 says

Four are the levels of speech that are measured, these the wise sages know. Three hidden in secrecy, they cannot manipulate, only with the fourth level of speech do humans talk.

So the sages of Rig Vedic period, composed mantras in such a way that different meanings can be perceived with different level of perception.

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only two meanings are perceivable to me.

1. If we take the meaning upwards for the word Udīcī, we will get SPIRITUAL meaning.

Indra removed the obstacles, so that the Shakti travelled from mUladhara towards sahasrAra, an upward journey, and the sage attained the BLISS .

1. If we take the meaning Northwards for the word Udīcī, we will get a historical meaning.

The river Sindhu might have changed its course towards North, which might have been allegorically mentioned in the Rig Veda. The sage of the mantra might be aware of this event or might have heard from his ancestors.

In Mahabharata thinning of the course of Saraswati was mentioned in many places. Similarly, the Sindhu river might have changed the course.

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Some paleo-environmental scientists have proposed that the Hakkra was fed by Himalayan sources, which made it a mighty river, but dried-up between 2500 BCE and 1900 BCE, due to tectonic disturbances which caused a tilt in topography of Northwest India, resulting in the migration of rivers.

According to this theory, the Sutlej moved westward and became a tributary of the Indus River, while the Yamuna moved eastward and became a tributary of the Ganges, supposedly in the early 2nd millennium BCE, while reaching its current bed by 1st millennium BCE.

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If changing of course of Sindhu is historical, then the age of Rig Veda would be the age at which Sindhu changed its course towards Northwards.