As has already been said, "They" has a long history in English as a gender-neutral singular pronoun. And I don't hear the people who object using "thee" and "thou" rather than "you."

There's also "that person," which I've heard mostly from 12-step people. But I've also heard it from a cop in London, Ontario (I'd called the police there because someone I knew on the Net had been sounding suicidal.)