Is the expression 'Never Meet Your Heroes' an adage?

One of the earliest instances of the expression to appear in Google Books search results in the title of a song by the Tenants, a Scarborough, Ontario band, which included the song "Don't Meet Your Heroes" on their 1984 album Visions of Our Future.

Anthony Holden, Of Presidents, Prime Ministers, and Princes: A Decade in Fleet Street (1984) [combined snippets] has this:

Some years later I had occasion to tell this story [of a newspaper account that rendered "bulges" as "bugles"] to a celebrated concert pianist, having discovered over a private dinner table the unlikely fact that he is an avid collector of newspaper misprints. At his London home he has a whole scrapbooks of them. Delighted though I was to meet the maestro, I did not wish to know this about him. I have never since been able to listen to one of his recitals with quite the same uncomplicated admiration. So I had learnt another useful early lesson: never meet your heroes.

A letter to the editor from Stephen Bray in Keyboard magazine (1988) has this remark [combined snippets]:

Oh, well, I guess that's life in the big corrupt city. I also guess that not only should you never meet your heroes; you shouldn't read their interviews either. I just turned the last page of your Todd Rundgren cover story to find myself described, albeit indirectly, as the "perfect example" of total vapidity, stupidity, and an obvious lack of any "real inspiration." It's especially funny to read that coming from one of the most powerful inspirations in my musical life.

An article titled "Real heroes?" in Madison Magazine, volume 31, part 2 (1989) opens with this lead sentence:

It has been said that you should never try to meet your heroes, lest they be found to have feet of clay.

Perhaps most intriguing is this instance from an article on A.S. Neill, the founder of Summerhill School, in the Advisory Centre for Education's Where magazine, issues 56–79 (1971):

On such experiences were based Neill's impatience with the academic, so often the enemy of the spontaneous and sincere. He had sickened of teaching — and especially of the brutal punishment of children in the schools — and had no wish to return to it. One of his heroes was H. G. Wells ('But never meet your heroes' — he found Wells in the flesh 'a brittle man'); and there's a touch of Kipps or Mr Polly about Neill's early adventures. He now, most briefly, became a journalist, editing a single-volume encyclopaedia; and would have been an inventor too if he'd had the capital.

Neill died in 1973, so if the quoted language expressed in connection with H.G. Wells is something he actually said, it is the oldest such quote in Google search results by a considerable margin, even if the relevant issue of Where magazine was somewhat later than the date of 1971 that Google Books claims for it.

Depending on how you assess the 1971 Neill quotation, the earliest match for "Never meet your heroes" may go back to 1971. It was beginning to appear in multiple contexts by the late 1980s.