Cycles, not years
One cycle is one full open and one full close. A standard torsion spring is rated at around 10,000 cycles. That is the number to divide into your own usage. A household that opens the door twice a day uses about 730 cycles a year, which puts a standard spring somewhere near thirteen years. A household with two working adults and a teenager, opening it six times a day, burns 2,190 cycles a year and will be replacing that same spring inside five.
What Las Vegas does to the number
Heat is the local factor. An attached garage in the Valley regularly runs past 120 degrees in summer, and repeated heat cycling accelerates metal fatigue in a spring that is already under permanent load. Airborne dust is the second factor: it works into the coils and into the bearings the spring turns on, adding friction that the spring pays for. Neither will halve the life of a spring on its own, but together they are why doors here tend to reach the end of their rated life a little early rather than a little late.
The warning signs, in the order they usually appear
The door gets slower or heavier and the opener sounds like it is working harder. Then it starts hesitating at the same point in its travel. Then it will not hold its position when stopped halfway. A visible gap in the coiled spring is the last sign, and by then it has already broken. Most doors give several weeks of notice if anyone is listening.
The balance test
Close the door, pull the emergency release cord to disconnect the opener, and lift the door by hand to about waist height. A correctly balanced door stays roughly where you left it. If it slides down, the springs have lost tension and the opener has been quietly making up the difference. If it shoots up, they are overwound. Either way it is worth a call before it becomes a breakage, and it costs nothing to check.
Getting more life out of them
Two things genuinely help. Lubricate the springs, rollers and hinges once or twice a year with a garage door specific silicone or lithium spray, not a general purpose penetrating oil that thins out and collects dust. And when you do replace, ask what it costs to move up to a high cycle spring. On a busy household the higher rated part frequently works out cheaper per year than the standard one.