Jimmy Baird is apparently still alive long after working on The Bob Hope Show and The Jack Benny Program and Jane Wyman Presents The Fireside Theatre and the rest before landing a recurring role on Fury in 1957.
But the OP didn’t come here for “apparently” – so I’ll promptly add that Jimmy’s big sister Sharon Baird did a better job of remaining in the public eye after spending '51 and '52 and '53 acting and dancing on The Colgate Comedy Hour: in '54 you could see her performing on The George Burns and Gracie Allen Show; in '55, she was acting on Damon Runyon Theater; and so on in the '60s and '70s and '80s and '90s and '00s.
(A lot of the '70s stuff was HR Pufnstuf/Lidsville/Sigmund and the Sea Monsters work, but, hey, that still counts.)
After making his TV debut on The Ray Milland Show, Joey D. Vieira had a recurring role on half-a-dozen The Pride of the Family episodes in '53 and '54; from '54 to '57, he had a recurring role on well over ninety episodes of Lassie; and he kept acting in the '60s and '70s and '80s and '90s and '00s, with a movie in the works for later this year.
Nicolas Coster – do an image search, and then say “oh, that guy” – has been acting in the movies and on TV since '53: '60s, '70s, '80s, '90s, '00s, '10s, you name it. Last year? Check. This year? Yup. Next year? The flick’s already in post-production.
Renée Asherson is still with us at 99, though: first TV appearance back in the '30s, most recent movie role in a Nicole Kidman flick this century, and plenty of pre-1957 work on both the big screen and the small one in between.
Jerry Maren was a frickin’ Munchkin in The Wizard of Oz, had his most recent movie credit in 2010, was the Hamburglar in between, and worked on the Andy’s Gang TV series back in '55 even if you don’t count how Superman and the Mole Men got turned into episodes of the show with George Reeves back when.
Oh, and he was the diminutive dad from the “Yada Yada” episode of Seinfeld.
Now in his nineties, Joe Kirkwood Jr was Joe Palooka in The Joe Palooka Story in '54 and '55 before doing yet other TV work in '56 (on Matinee Theatre) before spending the rest of the 1950s on The Red Skelton Hour and The Ed Sullivan Show.
Biff McGuire has credits on some twenty different TV shows in 1957 and earlier, with his most recent movie role circa last year; for the better part of a century, he’s been married to Jeannie Carson – who starred in Hey, Jeannie! in 1956 and 1957 after singing on The Jimmy Durante Show and doing a TV movie with Bob Cummings.
(Speaking of which, Biff starred as Josiah Blow in the Legend of Josiah Blow TV movie back in '52, and Jeannie was Heidi in a made-for-TV version with supporting roles for everyone from Natalie Wood to Wally Cox back in '55.)
Before doing The Jack Benny Hour in '59 and The Frank Sinatra Show in '58 – and before appearing in a couple of movies in '57 – Mitzi Gaynor was making the rounds on The Ed Sullivan Show and The Donald O’Connor Show and et cetera in the golden age of television, after racking up film credits all the way back to the '40s.
Richard Chamberlain almost counts, since he made his TV debut in '59. And he has a movie in the works for later this year with Sally Kemp, who picked up television roles in the '00s and the '90s and the '80s and the '70s and the '60s – and, yes, back in '57 was acting on Armstrong Circle Theatre and The Kaiser Aluminum Hour years after she first appeared on Robert Montgomery Presents.
Lonnie Burr was getting work on episodes of The Colgate Comedy Hour in 1950, and after some movies in '51 acted on The Roy Rogers Show in '52 and The Range Rider in '53, followed by decades of work in yet other movies and TV shows.
(How many other guys can say they shared the big screen with both Danny Kaye and Jean-Claude Van Damme? Who else has small-screen credits from ‘Medicine Man’ on The Beverly Hillbillies to ‘Strip Club Manager’ on Homicide: Life On The Street?)
Back before the first Mickey Mouse Club episode in '55, Cubby O’Brien was earning TV credits on Where’s Raymond? and The Hoffman Hayride; in '56, he was on the big screen with everyone from George Reeves to Iron Eyes Cody, after which he spent the '60s bouncing around from a Natalie Wood flick to an Elvis Presley flick before doing yet more TV in the '70s and '80s and performing on Broadway in the '90s and '00s.
I don’t see any mention of Don Keefer, who (a) got work on over a dozen TV shows back before '58 – Gunsmoke, Alfred Hitchcock Presents, The Phil Silvers Show, and so on – and who also (b) has a danged fun name to say.
WWII veteran Kirk Douglas made the rounds on What’s My Line and Name That Tune when he wasn’t busy on The Colgate Comedy Hour or The Jack Benny Program – all before '56, when he was tapped to serve as guest host of The Ed Sullivan Show.
In '57, he hosted the General Motors 50th Anniversary Show; in '58, he got his own This Is Your Life episode; and in '59, he became a TV producer with The Vikings.
Jean Darling of Our Gang fame is still alive – and still acting, as of last year – and could be seen on TV as far back as '52, on All Star Summer Revue.
Virna Lisa, who was so good with Jack Lemmon in How To Murder Your Wife, is still at work as of this year – a TV miniseries back in February, a movie currently filming, and so on – and in 1957, played Elizabeth Bennett in a made-for-television version of Pride and Prejudice before doing some TV movies in '58 (followed by yet another TV movie, plus another TV miniseries, in '59).
Wiki says nonagenarian Peter Sallis was in every Last Of The Summer Wine episode from 1973 to 2010, and IMDB specifies that he acted in a couple of TV movies and got work on television show after television show after television show before 1957, and I’d sure like to add that he’s of course Wallace of & Gromit fame.
Bobby Burgess was a dancer on The Lawrence Welk Show from '61 to '82, and before that he was acting on The Donna Reed Show in '58, and before that he’s got TV credits in '57 and '56 and '55, with his most recent IMDB appearance hitting last year.