[Doctor Stochastic]

Darwin was the first to assert that the earth was at least several hundred milion years old.

James Hutton had the idea earlier.

[js1138]

...indeed, he went rather overboard and asserted that the Earth was infinitely old...

That's certainly a long time, but Darwin had an actual estimate based on the observed rate of variation. Kind of off the cuff, but he was closer than either infinity or 6000.