My husband also has one of those jobs and could retire in five years (and re-invent himself). If he retires then his son will be 19. However, it was outlined in the divorce decree that he would pay child support until his son reached the age of 21 (to help pay for college cost). My fear is with the rising cost of college she will ask for more money.
I really think you need to get something official on paper now rather than later.