The beginning of Kaliyug. (3102 BC)
Starting with the age of Kali Yuga, it is 4,32,000 years. Till now
5115 years have passed. According to the Surya Siddhanta, Kali Yuga
began at midnight (00:00) on 18 February 3102 BCE. This is also
considered the date on which Lord Krishna left the earth to return to
his heavenly abode.
Kaliyug and Mahabharat war. Lord Krishna ascended to His Divine abode
at the end of dwapar yug and immediately kaliyug started in 3102 BC.
Krishn lived for over 125 years. He descended on the earth planet in
3228 BC. The Pandavas, after winning the Mahabharat war, ruled for 36
years and 8 months. Accordingly, the date of Mahabharat war comes to
Now about Vedic age, first we need to understand what actually Vedic age is, as stated here:
The Vedic Period or the Vedic Age refers to that time period when the
Vedic Sanskrit texts were composed in India. The society that emerged
during that time is known as the Vedic Period, or the Vedic Age,
Civilization. The Vedic Civilization flourished between the 1500 BC
and 500 BC on the Indo-Gangetic Plains of the Indian subcontinent.
So if you refer the above passage it conveys that during this period the Sanskrit texts were composed (Smriti) before that it existed (as Vedas are eternal) but were not composed, hence that period is termed as Vedic Age.
Difference between Shruti & Smriti: Shruti is “that which has been
heard” and is canonical, consisting of revelation and unquestionable
truth, and is considered eternal. It refers mainly to the Vedas
themselves. Smriti is “that which has been remembered” supplementary
and may change over time.
So basically the period which is before this Vedic period is termed as Pre-vedic period.
About Indus Valley age as stated here:
The Indus Valley Civilization was an ancient civilization located in
what is Pakistan and northwest India today, on the fertile flood plain
of the Indus River and its vicinity. Evidence of religious practices
in this area date back approximately to 5500 BCE. Farming settlements
began around 4000 BCE and around 3000 BCE there appeared the first
signs of urbanization. By 2600 BCE, dozens of towns and cities had
been established, and between 2500 and 2000 BCE the Indus Valley
Civilization was at its peak.
So if you analyze everything closely you can conclude that basically it started during Dwapar Yuga and continued in Kali Yuga as well.