Better with age
i belive wood age is more important - natural growth lumber that used to be available is much better quality than the farmed wood that is readily available today. I belive that makes more difference than the age of the wood
however wood ages, on a good quality insturment the resins in the wood get harder and the resonance changes, in most cases for the better, but cheap guitars can deteriorate because of warping or delamination of body peices. I have heard plenty of guitars that sounded better as they aged as well as others that sounded worse.
also pickups age, they loose strength and their crispness - this is good for hard rock, blues, jazz or cleans but maybe not for metal - i personally like aged pickups
In general the biggest factors in the sound of your instrument are in my opinion in this order ( excluding amps cords and effects )
- your fingers
-quality of woods used
-quality of electronics used
-pickup selection appropriate for the woods and bridge type and for your playing style / sound you are trying to achieve
- also the type of material your pick is made from (if you use one) can make a surprisingly large difference in your sound. tortex, polyethelene, celluloid, nylon, acetal, metal, wood all sound very different. I use tortex most of the time for a bright sound, celluloid if I want to melow my tone out a bit, and acetal ocassionally if I want an even darker sound.
Good post by the way, I whish there was more disscussion here about the technical aspects of what makes a guitar good.
My Carvin was built around 1985, I acquired it in 2008 and I believe its been sounding better and better with time. Might just be that I continue to grow fonder of her, but who knows? My stealth is much the same, although she & I have a bit of a love/hate relationship from time to time. Some days she just sounds thin & brittle and some days the tone is godly perfect.