Thats cool! That buck put on alot of growth on its last year!!!
To the question above...
A buck may never get extras and a buck can have extras from the get go depending on its genetics but yes... growth occurs with age... whether its mass, tine length, or EXTRA POINTS... it all increases with age as long as the buck is in its prime or in good health. A buck can also lose growth if its past its prime or in bad health.
I remember hearing from MuleyCrazy that theyve seen boone and crocket bucks at the age of 3. I think most bucks with good genetics will take more time than that in my opinion but dont dought it occurs.
Most bucks that have cheaters or extra points off their main frame are usually 5 yrs of age or older but extra points can be found on younger bucks just as easy.
A mule deer buck matures at the age of 3 and every year after that its capable of putting on more mass, tine length, and points up till the day it dies if it has good health and nutrition.
The character of a bucks rack such as fork depth, width, heigth, mass, number of points, EXTRAS, is determined by its genetics but its ability to put on this character is determined by age and time and is maximized by the nutrients and health it has during this time.