This Diamondback Rattlesnake's rattle is unbroken (button is present)
A Rattlesnake cannot be aged simply by counting the number of rattles on its tail. The tip of the tail of a new born Rattlesnake ends in a smooth rounded, slightly pear-shaped, "button," which is the first segment of the future rattle. As the young snake grows it sheds its skin, usually several times a year. Each shed skin adds a new, loosely overlapped and interlocked segment to the rattle. Shedding twice a year will add two segments to the rattle. Shedding three times a year will add three segments to the rattle. The more a Rattlesnake sheds, the more segments are added to its rattle. When the Rattlesnake vibrates its tail, the segments click together to produce the buzzing rattle sound.
The tissue that makes up the rattle is rather like a thin brittle fingernail. Just as a human can tear a fingernail, when the rattle gets longer than about 8-10 segments, some may break off and be lost. If the string of rattle segments ends in a smooth rounded button, all the segments are there and the rattle is complete. If the rattle string ends in a squarish or tiered nubbin, the rattle has been broken and some segments have been lost.
These two factors, adding segments several times a year and losing segments through breakage, make it impossible to tell a Rattlesnake's age by simply counting its rattles.