Is there any evidence that the gravitational constant is static?

How do we know the gravitational constant does not change with time? For example, it is adjusted by a powerful intelligent being (i.e. God) with a slower clock rate than us, in accordance with his will? Or maybe it just fluctuates for various reasons. This would throw the age estimate of the universe out the window.

Everything with a will is a bound infinity within boundless infinity. Isn't it the boundless infinity being synonymous with the concept of God?

By inductive reasoning.  One may question inductive reasoning like in the problem of induction.  The answer is either to accept it axiomatically or to say that God is one which implies that God is consistent which implies that inductive reasoning generally works.