I don't think Henry Fonda could ever have been classified a bit actor. In his first film, The Farmer Takes a Wife (1935), he gets second billing to Janet Gaynor. In 1939 he was just 34 years old and played Abraham Lincoln in Young Mr. Lincoln, a fictionalized account of the president's early life.
Let's look for other famous names in the cast. Milburn Stone played Stephen Douglas long before he became the doctor in "Gunsmoke." He was 35 years old while working on Lincoln, and this was almost his fiftieth role in movies.
Edwin Maxwell, who was Freedonia's Secretary of War in the Marx Brother's Duck Soup (1933), was in his 74th film here. In 1929 he started acting in film, and in ten years appeared in 110 films.
Jack Kelly was 12 years old playing a boy here. Of course he would become Bart Maverick much later on TV. Dickie Jones was the same age as Kelly, and his most famous roles were as a child actor. (Here we go again...back to Destry Rides Again!)
George Chandler had an uncredited part in this, his 165th film. I fondly remember him as Uncle Petrie in "Lassie" on TV. He has 444 roles listed on IMDb, and is remembered mostly for all the TV he did. I should blog about him in the future.
Let's not forget Ward Bond (again) and Donald Meek, who had a long career as a character actor in comedies with Mae West and W. C. Fields, Laurel and Hardy, Penny Singleton, William Powell and others, plus his wonderful role in Stagecoach as Peacock the whiskey salesman, and parts in so many other films. It's a shame we lost him in 1946 at age 68. Another future blog topic.