From ThePointsGuy.com…..
There’s one rental car cost that only age can help with: Once you turn 25, it’s a lot easier (and usually cheaper) to rent a car. For everything else, smart planning can help you avoid unnecessary hidden fees and costly oversights.
Like many travelers, I’ve made some serious mistakes throughout my journeys, and when it comes to renting cars, I’ve made almost every one of these on this list. Over time, I’ve learned the error of my ways, and you can, too (minus the expenses and headaches).