Are best sponsors are seasoned citizens, usually starting as total strangers. They have time to attend Mass & class with you. They are patient and usually know the Church, process, and catechism
… Is there an age limit on who can be your sponsor, or any other requirements?
your sponsor is to be an adult in good standing with the Church.
Also, is it a good idea to choose a girl you’re dating to be your sponsor? Completely hypothetical question!
Bad idea, I find catechumen rarely fight with seasoned citizens. Having emotions with spouses, siblings, in-laws, or coworker is more common. When we have husband wife pairs we switch them with others. We always try to have same sex pairs, so the wife is paired with another woman while the husband is paired with a man.
hope that helps