[altairprime]

I now like bitters and soda, and I didn’t like bitter as a kid, so I think there might also be shifts in favor of bitter unrelated to coffee. Perhaps the same thing that leads people to appreciate spicy or sour as experiences broaden.

[DougMerritt]

Years ago, somewhere I read that children have a genetically-based urge to avoid bitter flavors, since they may signal natural poisons, whereas adults can judge better, so the urge is lessened.

(And even if that source were true, that wouldn't make the genetic effect an absolute; it would depend on individual genetics and the variable expression of those genes. And probably on the individual's experience, either as a child or as an adult.)