The biggest changes start at maturity( 5-7yrs for WF) after that they just get more white and red with each molt.The white band will increase in area. The same for Yellow Front Sub-species (DYH,YNA,YCA,Pans,etc) except they lose green and gain yellow with each molt after maturity. My 42 yr old nape looks almost like a DYH with a dark beak ,LOL. And she just gets more yellow each year. i guess it's similar to us peoples "greying" with age. Generally they have more "color" the older they get.