I have never worked with anyone who is "like" me. There has always been some significant difference - age, gender, race etc and I think on reflection that its the way I like it because it helps me to have a stronger sense of who is me and who is the therapist - must be a boundary thing then. Having said that, I couldn't work with anyone who wasn't quick, intelligent, had a sense of humour and liked books.
Most important thing is that there is an alliance between you for the work to take place.