Physicists always debate on what actually was before the Big Bang. But on the basis of Big Bang theory, we can't describe the events before the Big Bang, as there was no 'time' before the Big Bang. Time started after the Big Bang. So the age of the universe is calculated from the moment Big Bang happened. Now let's find out age of universe according to Vedic Texts.
Brahma is known as the creator of the universe. While Vishnu is asleep, a lotus sprouts and inside which Brahma is born. Brahma creates the universe and even Brahma himself may be universe as well, that is why vedic texts call Universe as Brahmanda. This universe is not permanent, its temporary.
As per Vedic texts, our universe lives for 100 years of Brahma and right now we are in first day of 51st year of Brahma i.e. 50 years of Brahma have been passed and we are now on 1st day of 51st year. (These are Brahma years not solar years. Our modern calenders are based on solar years, 1 solar year = 365 days).
1 Kalpa (day) = 14 Manvantaras(Similarly 1 night = 14 Manvantara)
1 Day and Night = 28 Manvantaras
and 1 Manvantara = 71 Chaturyugas
1 Chaturyugas = 1 Satyuga(40%) + 1 Tretayuga (30%) + Dwaparayuga (20%) + 1 Kaliyuga (10%)
So 1 Brahma Year = 360 days and nights = 360 × 28 × 71 Chaturyugas
SatYuga = 1,728,000 solar years
TretaYuga = 1,296,000 solar years
DwaparaYuga = 864,000 solar years
KaliYuga = 432,000 solar years
1 Chaturyuga = 1,728,000 + 1,296,000 + 864,000 + 432,000 = 4,320,000 solar years.
So 1 Chaturyuga = 4,320,000 solar years
Now, first we will convert the 50 Brahma years which are passed into solar years(which are used in our modern calenders).
50 Brahma Years = 50 × 360 × 28 × 71 × 4,320,000 solar years = 154,586,880,000,000 solar years
50 Brahma Years = 154,586,880,000,000 Solar Years
Each Manvantara = 71 Chaturyugas = 71 × 4,320,000 = 306,720,000 solar years
So 6 Manvantara means = 6 × 306,720,000 solar years = 1,840,320,000 solar years
And now we are in 7th Manvantara, of which 27 Chaturyugas have been passed.
27 Chaturyugas = 27 × 4,320,000 solar years = 116,640,000 solar years
No we are in 28th Chaturyuga. Of 28th Chaturyugas, 1 Satyuga(1,728,000 solar years), 1 TretaYuga(1,296,000 solar years), 1 Dwapara Yuga(864,000 solar years) and 5112 solar years of Kaliyuga has been passed.
So 1,728,000 + 1,296,000 + 864,000 + 5112 = 3,893,112 solar years of this 28th Chaturyugas have been passed.
Of this 51st Brahma years; 1,840,320,000 + 116,640,000 + 3,893,112 = 1,960,853,112 solar years have been passed.
Of 51st Brahma Year = 1,960,853,112 solar years have been passed
Now total age of universe will be solar years of 50 Brahma years which are passed and the solar years of 51st Brahma year we are in now, which is equal to 154,586,880,000,000 + 1,960,853,112 = 154,588,840,853,112 solar years.
AGE OF UNIVERSE = 154,588,840,853,112 solar years
which is nearly 155 billion years
Earlier physicists claimed that universe is nearly 13.8 Billion years old. BUT after the discovery of dark matter and dark energy, physicists also claim the universe is nearly atleast 100 billion years old. Research is on! And I am sure Vedic texts will be proved rights this time also.