Most people actually prefer a dentist who has been established and successful longer. I am a dental assistant for two younger dentists (Pacific class of 2000) and we usually advertise without pictures of them so no one is automatically turned away. I also used to work for a Pacific grad from teh 70s. They are all fantastic, but attract different crowds. Younger people prefer younger dentists, but both older people prefer older dentists. The advantage of a younger dentist is that they are current with the latest technology and research, while an older dentist has done far more successful dental work. The best of both worlds is an older dentist who stays current with the latest research by continuing education and purchasing things like lasers, CEREC, digital Xrays, intraoral cameras, etc....
I guess the bottom line from my experience is older is generally more trusted in the field.