I don't think there's a rule written in stone about length of a personal statement. I've heard 1 page is good, with a max of 2, otherwise people get bored reading it.
Mine was a tad over a page, it was "personal", and all the program director's read it (I know b/c they commented on it, and liked it). Of course, I had it proofed before submitting it by the associate dean of psych at my school, he gave me great pointers. There's probably someone at your school in the psych department that helps med students apply to residencies.
BTW, I matched to the psych program of my choice. Good luck with your statement and with applying.