Granted, this thread really only makes sense if it's essentially about leading men and women. Character actors, by the very nature of their looks, often don't hit their stride until their thirties or later.

The ultimate example could be Lucille Ball, who was 40 when I Love Lucy went on the air and made her a mega-star. Before that, she was a well-known but not hugely famous B-movie actress.

Bea Arthur was 50 when she became an "overnight" success with Maude. She was well-known to NY theater audiences for years, but not to the public at large.

Jean Stapleton was 48 when she became Edith on All in the Family.

Except for Mary Tyler Moore, who was a star prior to her own show (thanks to The Dick Van Dyke Show), most of her MTM cast members, who all had been working actors, became household names beyond their 30s--and for many years to come after the show. You can instantly argue that Betty White was already known but before MTM, Betty was arugably better known as a game show contestant and as the wife of the game show host of the original Password.

Ed Oneal was in his 40s when he got the role of Al Bundy before that the only two memorable roles he had was in the short lived Popeye Doyle and a bit role in Dogs of War.

https://en.wikipedia.org/wiki/Burt_Mustin

Burt Mustin was an actor whose first TV credit was in 1951 when he was 67 years old, who became a popular character actor in a bunch of TV shows from the 1950's until his death in 1977. Mustin was in some plays and was a radio host before 1951, but he had regular jobs and acting was more or less a sideline and a hobby.

All the men of "Bonanza" except for Michael Landon were at least 30 or over before they "made it." Pernell Roberts was 31 Dan Blocker was 30 and Lorne Greene was 44 when "Bonanza" premiered. I think Lorne Greene had a prior career as a newscaster and was very successful before he was 30, but in news.

Three actors (leading men) that I can think of that seemed to get a pretty late start, when it came to fame and stardom: One is John Forsythe, who was already 34 when he got his first prominent lead, in 1952 in a movie called "The Captive City," and was already 39 years old when "Bachelor Father" started up. A second example would be Darren McGavin, who was dabbling in live-tv in the early-50s, but didn't really hit it big until he starred as "Mike Hammer" in the tv-series in 1957, when he was 35 years old. A third would be Richard Boone, who started out mainly as secondary villains in films of the early-50s, when he was in his mid-30s. He was already 38 when he started starring in "Medic" in 1954, and then, 41 years old when he really hit tv-stardom with "Have Gun Will Travel in 1957.

All the men of "Bonanza" except for Michael Landon were at least 30 or over before they "made it." Pernell Roberts was 31 Dan Blocker was 30 and Lorne Greene was 44 when "Bonanza" premiered. I think Lorne Greene had a prior career as a newscaster and was very successful before he was 30, but in news.
Yes. Lorne Greene was a newscaster for the CBC (Canadian Broadcasting Corporation).

Angela Lansbury in Murder She Wrote. She became a house hold name at 58 or so. As for Jean Stapleton, was she in her 50's in All in the Family? I had her about mid 40's on AITF.She must have been older than Carroll. Isabel Sanford of early All in the Family days was middle age too.

Granted, this thread really only makes sense if it's essentially about leading men and women. Character actors, by the very nature of their looks, often don't hit their stride until their thirties or later.

The ultimate example could be Lucille Ball, who was 40 when I Love Lucy went on the air and made her a mega-star. Before that, she was a well-known but not hugely famous B-movie actress.

Bea Arthur was 50 when she became an "overnight" success with Maude. She was well-known to NY theater audiences for years, but not to the public at large.

Jean Stapleton was 56 when she became Edith on All in the Family.

Except for Mary Tyler Moore, who was a star prior to her own show (thanks to The Dick Van Dyke Show), most of her MTM cast members, who all had been working actors, became household names beyond their 30s--and for many years to come after the show. You can instantly argue that Betty White was already known but before MTM, Betty was arugably better known as a game show contestant and as the wife of the game show host of the original Password.

Actually, Stapleton was only 48 when she "became Edith". She was born in 1923, and the show premiered in 1971.