hhmmm....  Hard one!

I think its best to try and make a joke of it and just say you don't date older men, or say you're not rascist but only date people from your own country!

Try to keep it jovial but clear! so that no-one has to feel uncomforatble afterwards!  unless you don't like your job ofcourse!  If that's the case tell him to stick it where the sun doesn't shine!