If you've pushed past the half-century mark, the age of carefree traveling is over.

This doesn't mean you shouldn't travel at all. Far from it. The most recent surveys show that 70 percent of persons hearing retirement are planning trips of up to two months duration, according to Robert Custer, director of retiree relations for the Sun Company.

But things do change as we grow older. And the first to admit it are senior celebrities who were born on the road and have been living out of suitcases much of their lives.

If you watch the PBS television show "Over Easy," a daily half-hour program about aging, you often have heard celebrity guests remark on the pitfalls they've learned to avoid while traveling. Off the air, they remember "something pertinent about the elderly and traveling, then kick themselves for not sharing it with our listeners," says "Over Easy" host Hugh Downs.

Downs passes on some of these off-the-air travel tips:

RAY BOLGER: "I never travel abroad without seeing my dentist first; at my age a toothache in a foreign country can be costly," the 73-year-old dancer-come-dian said. "You stand a good chance of losing the tooth because the accepted treatment in many places is extraction -- period. Also, be sure to carry a copy of the prescription for your eyeglasses. In fact, take along an extra pair of glasses.

RUTH GORDON: "Always pre-test your clothes; I learned the hard way," the 82-year-old actress said. "I once bought a pair of shoes in New York and wore them for the first time in London. Within hours I had sore feet and blisters, something I certainly didn't need at my age. Also, if you're going to hot climates, synthetics like Dacron and nylon may be easy to launder, but they donht absorb moisture well."

GARSON KANIN: "When I was working on my book, 'It Takes a Long Time to Become Young,' I came across a lot of helpful hints that I never got into print," the 66-year-old author said. "For example, cardiac patients should avoid altitudes of 5,000 feet or over. Some other people can't even take that altitude; they suffer chest pains and shortness of breath."

Kanin, who is married to Ruth Gordon, also noted that all medicines "should be in plastic bottles because they weigh little and are less likely to break.

"When carrying liquid medicines (capsules or pills are preferable), tape the cap with adhesive and wrap the bottle in a plastic bag." He also warned that Medicare only covers hospital and doctor bills in the United States, the U.S. Virgin Islands, Puerto Rico, American Samoa and Guam.

Downs, 57, has this travel advice from other guests who have not yet reached 60:

GLORIA DE HAVEN: "Twenty-five years ago, two women never would have thought of touring alone across America in a van. I've just completed a trip with a friend that started in Miami and ended in Los Angeles. We had a wouderful trip that was most enjoyable because we observed a few rules of common sense."

The actress, 53, said the main thing to avoid was driving late. "It adds to driver fatigue, makes reactions slower and senses duller. And you're really not gaining anything by it. It's much better to stop early, have a leisurely dinner, relax before retiring, get a good night's rest, and get an early start. Even the Grand Canyou looks like nothing in the dark."

JANET LEIGH: "I never drink tap water when I'm in some little town outside the United States or Northern Europe," the 51-year-old actress said.

Sen. EDWATD KENNEDY: "I would advise any elderly person taking a trip to see his or her doctor first. Get a checkup. Also get any prescriptions you might need. Ask for the generic or chemical names of your medications; this allows you to identify them for foreign physicians should you need medical care. Obtaining a summary of your medical history is a good idea, too. In emergencies, it's helpful to have your doctor's telephone number so he can be contacted." Kennedy, 46, is a member of the Senate subcommittee on aging.