[quote=@vancexentan]
[@Cu Chulainn] That I don't believe so. Rin is in the top thirty mages in the association's history and she was born with that talent. You'd either need to be very old, or have done something big to get that sort of magical power. At most I believe two would be sufficient for a character. Three seems to be pushing into expert territory.
[/quote]

An elemental affinity basically dictates what element or elements your magic circuits are attuned to, and your affinity to an element is, in a way, affected by your origin. So for the most part, magi are born with said talent. 

This is based on research and implying multiple sources into one undeestanding. Judging from this all, I don't think an affinity is gained from experience, but from having a knack for magecraft involving said element.