Depends on the quality of the fiddle.

There's plenty of cheap fiddles out there which are no more than plywood with a veneer on them. (off the subject completely, Leonard Cohen talks about "a monkey and a plywood violin" in First We Take Manhattan. Low concentration span? Me? What did you say again? ;-) These won't improve noticeably with age, and the veneer probably won't change that much looks-wise.

If you get a decent instrument though, it will age nicely. And generally, the heavier the instrument, the richer the sound - my fiddle's about twice the weight of my friend's, but the sound has so much more depth to it. But then mine was my granny's. They don't make them like they used to...

Grab.