I have never seen a "mature" spike in my life!
Believe it or not but it sometime does happen even in moose another member of the deer family.. Sometimes because of genes and sometimes because of food. A friend had found a spike drop from a moose a couple of years ago that was clearly from an adult moose. The spikes were both around 3 feet long. Another one was shot that was around 800lbs dressed that had long spikes, the same thing with deer! It can and does happen from time to time... Though the majority are just young bucks..