Skipping down from the OP …
I’m fine on 17 of the 23. The other six:
My age: early 50s.
Geez … almost all the names I whiffed on guested on The Muppet Show at one time or another. I watched plenty of The Muppet Show, so I guess those people didn’t sink in.
And I whiffed on Avery Schreiber’s kids (not Liev Schreiber) and I missed on the spelling of Azvanour’s surname.
Had someone showed me a picture of Avery Schreiber cold this morning, I’d have thought it was former Today show movie critic Gene Shalit.
I rescued Phyllis Diller from a snowbank when the Rolls Royce she was riding in got stuck.
I know all the rest but maybe one or two.
Schreiber was on TV a lot in the '70s, including ads for Doritos, but yeah, he and Shalit had similar hair and bushy mustache.
It’s Bruce Forsyth, BTW. Not Forsythe.
Oh 
I’m 52 and Aznavour, Ballard, and Forsyth are the only ones I know solely because of why they’re on the list. Everyone else I’m familiar with. It makes me wonder, though, who did I likely I know when the show first aired? Probably it would have been
Ruth Buzzi
Rita Moreno
Jim Nabors
Florence Henderson
Paul Williams
Sandy Duncan
Avery Schreiber
Phyllis Diller
Vincent Price
Valerie Harper
Twiggy
Mummenschanz
I missed three. They’re all people I saw on tv or in the movies. I recognized Bruce F. because of Strictly Come Dancing. I never saw his early work on the BBC,
Age early 60’s. I rarely watched the Muppets.
It’s funny that I don’t remember the names of contemporary actors. I’ve seen recent films, but never pay much attention to who is in them.
I read the list to my mom. She didn’t know what they had in common, but she knew who they all were. Of course, she’s also 86 …
Never heard of: Charles Aznavour
Recognize the names, can’t remember who/what they are:
Bruce Forsythe, Kaye Ballard, Mummenschanz
Instantly got all the rest. I’ll be 72 in five months. George has been my favorite Beatle for 58 years.
Yes, I got 18 of these.
I’m 50 years old.
It looks like “70s celebs who appeared on Hollywood Squares at some point…?”
There may be more than one famous Bruce Forsythe, but if it’s the British game show host, I’m not sure how he ended up on that show…
It’s curious to me that so many people haven’t heard of Aznavour. As a small town kid in the midwest growing up in the 60s, even I was exposed to him as he made the rounds of US talk shows (Carson/Douglas/Griffin) around that time. Well, that’s just me, I guess.
Oh, should have noted the Burns & Schreiber connection. Jack Burns had been a producer on The Muppet Show.
Now I’m going to be thinking all day about atheistic communist frogs bred in Cuba eating people in Florida. When was the last time you got a call from Tampa?
It was, indeed, the British presenter. As noted earlier in the thread, although Henson and the Muppets were American, The Muppet Show was produced in England, by an English TV studio, and that likely explains the presence of both Forsyth and Aznavour (who were undoubtedly not well-known at all in the U.S. in the 1970s) on the list of hosts.
They could be radioactive, too!
Gabe Kaplan had a similar “bushy black hair and mustache” look in those days.
I got 18 because I don’t recognize some of the recent names. Your list needs to reach back further - William Bendix, Bob Trout, Gabriel Heater, Dionne, Jack Armstrong, Jack Doc and Reggie, Lum and Abner, Rochester, Harold Perry, Mercedes McCambridge.. Stuff like that.
I’m in my 80s.
Yes and I remember watching it with the familiar ATV ident and being a little perplexed because the Muppets were ostensibly American. Makes sense!
Forsyth’s catch phrase was a call and response where he would say “Nice to see you” and the crowd would reply “to see you, nice!” He hosted a bunch of game shows like Price is Right and Card Sharks, IIRC.
What I find hilarious is that while I recognized most of the names, the source of the list eluded me – in spite of the fact that I watched the first half dozen or so episodes of the Muppet Show just a few months ago on Disney+. 
If you’re 57, then almost all those people are people you’d have known independently of the Muppet show, so they don’t stand out as “Muppet guests” just as “people anyone of a reasonable age would recognize”