"Body marking of category, age, or division, is not required by the Competitive Rules. Only race number body marking is required. Identifying each athlete by division or category is optional for race directors. Accordingly, your should address your concerns to the individual event organizer where you compete. The race director may very well be able to accommodate your request and be happy to do so."
So there you have it! You really don't even have to have your age, just your race number! My apologies to Sarah for being thoughtless and embarrassing her, prompting the discussion at the race!