The snake of real concern here in Arizona is the Western Diamondback. It has definitive diamond shapes running the length of the snakes body. They are generally a light mottled tan color with darker colored brownish diamonds. A rattlesnake is clearly defined by the rattles at the end of their tail. These rattles are caused by the last piece of skin left behind during the molting process.
Snakes molt in order to grow and they molt many times the first year of life.
For this reason, the number of rattles doesn't necessarily identify it's age. Rattlers may have jaws that are wider at the hinge than at the opening. This is to swallow larger prey. They emerge from hibernation when temperatures beginning to warm sometimes as early as late March in the warmer regions of Arizona. They migrate from their winter homes in search of food but rarely go more than a mile from their den.