Name a specific skill you'd have to be good at to be a professional...
its a skill level not a specific age
There is not set amount of money that a professional girl volleyball player will earn. This depends on age and skill.
Sector specific skill
Depends on his level of skill If very professional only at the pitch If low skill he normally has a sidejob unless it is enough to live of
To be a pro baseball player in takes heart, determination, skill, plenty of hard work, and perserveriance
communication skill and technical knowledge
No. Bingo is a probability game so it is not possible to make a living playing it. This contrasts with games of skill like poker where it is possible to be a professional.