This is an excellent article on Martin Milner from The Lima News (based in Lima, Ohio), dated October 15, 1960. I've read several articles on Milner from this period and they all seem to play up his family. He had a young wife named Judy and a two-year-old daughter named Amy and when the show premiered in 1960, his wife was pregnant with their second child.
Milner and Maharis were a real study in contrasts, just as their characters Tod and Buz were. At the time, nobody knew that Maharis was gay (he was still way inside the closet, as most gays were in 1960). Newspaper writers in the early 1960s, therefore, did not emphasize this point. But they did focus on other differences: Milner was a more experienced actor than Maharis. Maharis also happened to be a singer (and a damn good one), but Milner wasn't. Maharis was from a working-class neighborhood, but Milner tended to be more middle class (he was born in Detroit in 1931, but his family moved to Los Angeles when he was fourteen and hired a personal acting coach for him). He landed a part in the 1947 hit Life With Father (starring William Powell). Milner would go on to attend the University of Southern California for a time, then he'd join the Army and eventually, in the 1950s, return to acting.
The rest, as they say, is history.