Based on their current schedule - 6x weekly JFK, 4x LAX, 4x LAS, it can be done with just two planes if everything goes well. But according to planespotters.net they have 3 762s in the fleet now, so it really shouldn't be this bad.

But anyways, their three 762ERs were originally delivered in 1984, 1985 and 1988. Average over 21 years old.