SO WHAT, we observed in what we thought was a jaunty way, when questions were raised as to whether the new British ambassador to Washington, Peter Jay, was too young (40) for the job, and whether his predecessor, Sir Peter Ramsbotham, was too old (57) for the Carter crowd. President Carter, we noted, is 52, Secretary Vance is 60, Amy is 9 - so what? So maybe we spoke too soon. Not about Sir Peter's being too old for the Carter administration, mind you, or about Mr. Jay being too young for such responsibilities. What worries us is whether we may not be too old for Mr. Jay. Frankly (and we are not here referring to the fact that this year we are celebrating this newspaper's 100th anniversary), we cannot remember a British ambassador in the last several decades who has introduced himself to this country quite the way Mr. Jay presented his credentials, so to speak, to Sally Quinn in the Style section of this newspaper the other day.

Turning 40, Mr. Jay said, was a real "psychotrauma." And he went on: "Like every man with a Peter Pan complex, seeing himself age, I went into the darkest gloom . . . then I came through it. I said to myself, 'okay, I'm middle aged, I'll adjust myself to the fruits of middle age.'" And then, "suddenly this happened and all the world clamored over my youth. It was total reversal of self-perception."

Now when Mr. Jay spoke of "all the world" clamoring (or when Ms. Quinn observed in her account of the interview that "everyone in Washington" knows of Mr. Jay) it is only fair to note that both were not talking literally; the reference, presumably, was to what has come to be known as le tout world (or le tout Washington) - le tout being a phrase much in use in contemporary journalism to define a special, you might say trendy, slice of society. We bring this up only by way of explaining that it was almost certainly in the context of a certain trendiness that Mr. Jay was - or probably thought himself to be - speaking.

Even so, there was something in these opening remarks of Mr. Jay's, and in many others, that struck us as a departure from the norm - a metaphor, you might say, on the current state of both journalism and diplomacy. Somehow, reaching back at random and diplomacy. Somehow, reaching back at random over the years, we can't remember Lord Halifax, for example, or Sir Oliver Franks, or Sir Roger Makins or any of HM's recent envoys to Washington, forthat matter, presenting themselves in quite so forthright and freewheeling a fashion, and on such a rich variety of subjects.

Does he smoke? "I'll smoke anything . . . it scares me to death. It's more a fear of losing youth . . ." Is he trendy? "I recoil from putting myself in boxes . . . I'm not a brand of soap." Is he arrogant? "I know I'm not arrogant in my mind and in my heart . . . I don't feel arrogant." Has he been to a psychiatrist? "God no . . . I think that is profoundly unhealthy. Wild horses wouldn't drag me."

There was more, of course - much more - and what particularly puzzled us about it was not so much the questions that were being asked as the ones that were being answered. That, and the particular way they answered. Now a case can be made, of course, that when Mr. Jay speaks of arrogance (or the lack thereof) in the heart, he is talking Carter Talk. And his introspective musings, in public, do put you somewhat in mind of Andrew Young. Could it be that Mr. Jay has a better sense than some of the rest of us of Jimmy Carter's Washington and the New (Confessional) Diplomacy? Or is he, perhaps, merely trendy? We will know more later, when he gets down to the serious business of being an ambassador.