Double-A wrote:

This is easy to reconcile.  We know from SR and GR that the rate of
time flow varies, depending on your inertial frame.  High velocity and
gravity make clocks run slow.  Whose clock is right?

The universe could be only 6000 years old, if God has a slow clock!

Nope.  Everyones clock is right.. they only vary if different clocks in different frames are compared later.  The clocks aren't wrong, they just all read different.