Tony Danza was I want to say, about 31-32 when Who's the Boss? premiered in the fall of 1984 (they actually shot the pilot in late 1983). And Alyssa Milano was about 11-12 in that same time frame. If I remember correctly, it is explicitly stated by Mona at the very end of the series (in spring 1992) that Tony Micelli is 40 years old. And Samantha was pretty much, the same age as Alyssa Milano was in real life at the time. So she was 19 when Who's the Boss? ended.

Dates of birth: Danza - April 21, 1951; Milano - December 19, 1972

So in real life, Danza was 21 when she was born.

I also wonder if they sort of skimped around with Tony's age. In the "Samantha's Growing Up" (https://www.imdb.com/title/tt0747814/reference/) episode from Season 1 (1985), it's stated that Tony is 30 years old. And yet, by the end of the series (1992), Tony is said to be 40.

I didn't know this until I read this article (https://www.msn.com/en-us/entertainment/entertainment-celebrity/tony-danza-reflects-on-wrong-turn-in-his-career-after-who-s-the-boss/ar-AA1TQeRg?ocid=msedgdhp&pc=U531&cvid=696087920d3f4bb2a0decb59321db7aa&ei=16) about Tony Danza, but it says that his son Marc is currently 54 years old. And Tony himself is now 74 years of age. So, Tony at the very least, had to have been about 20 years old when his son was born.