Pretty much any color, including orange, is not static in goldfish. Goldies exposed to natural sunlight tend to keep darker colors longer than than their tank kept siblings though. Private breeders will breed selectively based on genetics (rather than profit of a commercial fishery) to maintain greater stability of certain colors as well but these fish also have hefty price tags. Its not so much of a fish 'getting old' but more so just simply nature. Even babies will go through various color changes.