First of all, Kamaka at one stage used gold-coloured labels. Which might be confusing, but I understand we mean something different here, the best years of construction.
Secondly, age and playing can improve the acoustic qualities of an acoustic instrument, and it certainly executes a certain natural selection: good ones get passed on, bad ones dissappear.
In response to a statement above: good instruments weren't always appreciated as such, and not certainly in monetary value. Sentiment, resale value, publicity, ignorance, rarety all are disturbing factors. In new instruments, the price usually reflects the quality, in antique instruments not necessarily so - hence Bill Monroe's chance of finding a Loar-era Gibson mandolin at a discount price.
And also, remember that that mandolin was sold by an Italian barber, who didn't prefer the higher-pitched, lightning-speed action a mandolin needs for bluegrass music, but probably wanted a deeper-sounding, echoey bowlback for playing Italian dance riffs. What is 'good' depends on genre, taste... or on your expectations, really. Are you looking for the loudest Kamakas, or the deepest sounding ones, or sturdiest ones? Some of the commenters above state that the current myriad of models on offer, clearly defines a 'golden age'. Which is very true, if a broad choice is what you need. In sheer production numbers, I think Kamaka themselves also have stated that their golden age is now: stock's flying of the shelves, they need new hands to keep up.
When I narrow it down to sound alone, I think the most pleasing to me are the 1950s-1960s Kamakas, especially the pineapple ones. Not extremely valuable, a bit of an acquired taste, probably not as refined as current models, no great variation in sizes, nothing special cosmetically, but 'best in show' nonetheless.