There's alot of mystique and maybe a bit of romance attached to the value of certain woods for guitar building, and it's probably has more to do with what people believe than scientific research. I know that certain types of woods have cetain tonal and accoustic properties, but I'm not sure how much the age of the wood affects electric guitars, accoustic guitars, I think are affected alot more by the quality of the wood, and wood quality is one area that comes into play alot with old woods, alot of species like Brazillian Rosewood, Cuban Mahoghany, Gabbonese Ebony etc... either can't be harvested legally, or can't be found in quanity to make instruments, unless you get access to the stockpiles of antique lumber, the old stuff also has the advantage of usally being a better example of a species, old growth, older trees, bigger trees etc, but still does it make a better sounding guitar? It's hard to say, there are just too many factors, I think the best bet is the skill of the guitar maker, knowing how to make a fine sounding instrument has got to be, as, if not more important than what it's made from............