According to Hubble's constant how old is the universe?
13.8 billion years
It is a scientific surmise that, yet to be identified precisely as what matter it is, Dark Matter prevalent within and in-between galaxies is surmised as responsible for the expansion of our universe. The Hubble constant is a measure of the rate of this recession that causes expansion of our universe..
There are 3-sd approximations made in this decade that give this constant in the range 71 km/s/mega parsec down to the current estimate of 67.6. From the reciprocal , the age of our universe is estimated as 13.8 billion years.
For this estimation, the units km/megaparsec in the Hubble constant have to be converted to light year (ly) / ly and time unit has to be converted to year, from second.
For sources, refer to the earlier WMAP NASA project and the later ESA Planck Mission.