would it be possible to find a galaxy 20 Gyr away if the universe is supposedly only about 15 Gyr old?

Answer 1

It is possible that there are Galaxies 20 billion light years away from us, at the present time, because the universe is expanding and has been expanding throughout its history. While we see a universe no larger than 15 billion light years in radius, we are seeing objects far away from us at positions they occupied a long time ago.

It is estimated that the objects visible to us are now up to 46.5 billion light years away.

Also, since the universe underwent a period of hyperinflation shortly after the big bang, there are object outside of our range of vision, which we will never be able to see. It is estimated that the radius of the entire universe must be at least 78 billion light years.

Answer 2

You mixed thing up a little.
Is Gyr now supposed to be a unit of time or a unit of length? Both seems a bit odd to me.
Though, the other answers seem quite correct to me!

Answer 3

No, it would be impossible because the light will never reach Earth. Beyond 14,000,000,000 light-years away, the Hubble expansion rate of space is greater than the speed of light. Also, for a time after the Big Bang, spacetime was opaque; for that reason it's impossible to image the Big Bang as well.

Answer 4

the universe is believed to be about 13.6 billion years old, with galaxy formation beginning a couple of billion years later, so no. Hubble hasn't seen anything much farther back than about 11 billion years or so, other observatories back to about 13.