ONE OF THE WONDERFUL things about writing a newspaper column is that you get to say what you think about matters that are sometimes none of your business. It is in that vein that I bring up the impending marriage of Lady Diana Spencer to Charles, Prince of Wales, heir to the throne and all of that. I'm against it.

I should point out right away that I know neither Charles nor his intended and my only familiarity with the royal family is limited to a few moments spent peering through the gates of Buckingham Palace. But a few moments is all it takes ti realize that what may look like a palace on the outside, can amount to a jail on the inside. Where Lady Diana is about to go, there is not exit.

I suppose I have the standard American ambivalance toward royalty. I sort of like it -- over there. I like all royal families -- english, Saudi Arabian, Jordanian (although not very much) and even those in exile. I find them essentially very amusing, diverting and silly, like a good operetta. but there is nothing amusing or silly when the conventions or royalty conspire to have a 32-year-old man marry a 19-year-old girl. If Charles were not a prince, he would be a dirt old man.

Okay, Charles is a bit young to be called that, but the fact remains that Lady Diana is nothing more than a kid. Take away the title of Lady and what you have is a teen-ager who is about to marry a man 13 years her senior. She knows little of the world. She has been boarded and tutored. She teaches kindergaten. She lives with three other women. She drives a little red car and is about to marry a man who can, as someone once wrote, "command a ship, pilot a helicopter, drive a tank, pilot a jet, parachute out of one and is fully trained as a frogman and commando." But for all of that, he will be a failure as both man and monarch if he can not coax an heir from his bride. They are both trapped in their roles.

Hers, though, is the real trap. She is about to enter a life of cutting ribbons, sitting with legs crossed at the ankles and, God and passion willing, producing heirs to the throne. You could train a horse to do much of this, but a horse, it goes without saying, would not have to suffer the glare of endless publicity. It is Lady Diana's fate to live in a nation that has the most rapacious and boorish press imaginable -- a columnists in every car, a photographer behind every potty and the man from the Daily Mail crashing through the skylight.

It is this press, in fact, that has all but insisted that the new queen be what only one previous queen remained, and then only in legend -- a virgin. There is no room for scandal here. This is no place for women who have pasts -- who are, in a true sense, women. Those who have been linked to Charles (UPI says there have been 40) have been chased and investigated and photographed. Their lovers have been induced to come clean, the gossips to gossip. In one case, a woman confessed that her husband left her for a woman who was even then, in fact or fancy, linked with the Bonnie Prince. With a press like that, it is a wonder he stayed bonnie.

So what we had was a nation embarked on some sort of search for a child bride -- for a virgin. It is almost medieval, a true return to the old days. But the upholder of conventional morality is no longer the Church, it is the press and the Bulls are not papal, they are journalistic. The only woman to qualify, the only woman who could marry the future king, is a woman virtually without a past.No mature woman, no woman of experience who had lived out in the world alone, who had had a career, could possibly be considered. She might have . . . God forbid. . . .

But a woman so young, so inexperienced, so unwordly is not prepared to decide if she should be, for now and evermore, the queen of England. There are no trial separations and there most emphatically are no flings. For royalty, marriage is forever, irrevocable -- a sentence rather than a continuing option. There is, after all, no divorce for a king and queen. What Lady Diana Spencer needs is not a summer wedding but a few more years. After all, she's no lady. She's just a kid.