There are fifteen major keys that cover the 12 pitches in any octave. So if a soprano sang a particular song in G, so could a tenor or baritone - just an octave lower. Determining what fits who is also a matter of the range of the song, not just the key. They are no special keys just to fit women or men. Trained people determine ahead of time what key they wish to perform a certain song in. Karaoke is a roll of the dice - far less choices are provided. In voice class, I could by memory play every assigned song in every possible key, in the spot - as could all similarly educated teachers, or professional accompanist for singers. It is our job. We all can do it.
Multiple degrees in music - taught Voice and Choir in schools of NY for 30 years.