It is a set thing when he is recruited. It is not about age, but years fighting. It use to be 5 to 15 years, but was changed to 7 to 15. That is from the day he is recruited. My best three fighter ever retired at between 5 and 7.5. The retirement time is all ready set when your fighter is recruited.
I left you a few notes, hope you do not mind. The two most important thing are style, and weight. Always try to fight at the lowest weight your fighter can cut to. Some guys can cut 25+ pounds. Others can't cut 10.
Grrows team