Does darker bourbon mean it's older?

Color in bourbon comes entirely from the charred oak barrel; federal rules prohibit adding caramel coloring to straight bourbon; so it's genuinely tied to wood contact. But "more time" is only one of several things that drive how much color a barrel gives up. The char level (how deeply the inside of the barrel was burned, from a light Level 1 to a heavy Level 4 "alligator char") changes how fast color and flavor extract. So does where in the rickhouse a barrel sat: a barrel on a hot top floor can pull deep color out of the wood in a few years, while an identical barrel on a cool lower floor takes much longer to reach the same shade.

Put two barrels side by side; one young and hot-floor, one old and cool-floor; and the younger one can easily look darker.