I think you may be mistaken about the range for carbon dating. After two half lives, 1/4 (1/2 of 1/2) of the C14 would remain, and after three half lives, 1/8 would remain, which should still be measurable. If I remember right, I believe C14 dating is usable out to about 60K years, but with a large margin of error when you get out that far. You're still right about it not being able to date something as millions of years old, though.