Gordon White is 79. Kevin Chang is 24. Both recently tried to rent cars but ran into trouble because of their age.

White’s online travel agency warned him that he might be too old, and Chang had to pay more for his vehicle because of his youth.

A quirk of the auto rental business? Hardly.

Other parts of the travel industry, from airlines to hotels, routinely segment their customers by age. The experiences of White and Chang underscore an often overlooked detail for anyone traveling: Age matters more than you might think.

White, a writer who lives in Deltaville, Va., reserved a car in Glasgow, Scotland, through Expedia. After he finished the transaction online, a window popped up on his computer screen warning him that some international car rental agencies do not rent vehicles to older drivers.

“That just about floored me,” he says. “I can understand that some older people probably shouldn’t be driving, but honestly, I am not one of them.”

Chang, an engineer based in Chicago, has the reverse problem: When he called his travel agency, he was told that his car rental company, Budget, added an underage fee. It doesn’t rent to drivers younger than 21, and renters younger than 25 have to pay a surcharge. But, a representative told him, the travel agency had made special arrangements to have the fee waived.

Nevertheless, when Chang picked up the vehicle in Buffalo, Budget tacked an $80 fee onto his bill. He protested, to no avail. “They denied our request to waive the underage fee,” he says.

The subject of age is a touchy one for car rental companies, according to Sharon Faulkner, the executive director of the American Car Rental Association. Companies don’t have formal age limits in the United States, because they would violate discrimination laws. “But they do for the underage driver, citing insurance regulations,” she adds. (New York, with its “must rent” laws for drivers 18 and older, is one exception.)

If you’re renting a car, it’s difficult to get around the rules. Faulkner says that every rental car company will ask to see a valid license and will punch the holder’s name, address, age and license number, with the expiration date, into its system. “If there is an age limit — under or over — and the rental company has added these limitations to their Web site and therefore loaded that into their computers, then the computer will alert the rental representative that the contract cannot be completed unless a fee or a manager overrides the system,” she says.

To make sure that you’re not affected, she advises that you call your car rental company before you pick up your vehicle. That’s what White did when he rented in Glasgow. When he reached the location by phone, a representative told him that there was no age limit, and he rented from it without incident.

Chang received only a $50 refund from his travel agency.

This kind of discrimination happens so often when we travel that we hardly notice it. Some of it is helpful, such as lap children flying free on planes or senior citizens receiving discounts on restaurants, national parks and other attractions.

But much of it is also discriminatory. Try renting a hotel room if you’re under 21. Many hotels won’t rent you a room, and some state laws allow them to show young people the door. Likewise, some package tours are off-limits to people over a certain age, although tour operators are reluctant to say so. Usually, they just steer elderly travelers toward another trip, hoping that they’ll take the hint.

Even the federal government is in the age discrimination business when it comes to travel. The TSA recently adopted special screening procedures for children younger than 12 and adults older than 75, allowing them to keep their shoes and light jackets on at the checkpoint. How do agents know that you qualify? They conduct a “visual assessment.” Good luck with that.

Of course, there are good reasons for discriminating, at least from the perspective of a business. Any innkeeper can tell you that younger hotel guests — especially those checking in during spring break — can be trouble. Or that the under-21s have a greater chance of getting into a fender-bender in a rental car. But it’s also true that many younger and older travelers are safe and responsible. Do they deserve to be treated differently?

If there’s a takeaway for the rest of us, it’s this: Age matters when you travel. It may save you money, but more often, it will be used as an excuse to charge you more, or deny you a service to which you should have access.