I think 12 years old it too old to have a boyfriend. 15 maybe, but still a little too young. I can understand liking a boy at that age, sending notes and having lunch at school, but other than that, no I would not endorse it with my child. I think 16 is a great age to start dating, going out but once you have had "the talk" with your child and have spent enough time nuturing them, so they make good decisions in the dating world.
There are just too many young women out there that get caught up, get pregnant, etc. I also believe healthy honest communication is key. I remember a young witness girl I grew up with, her JW family told her "don't do it", no discussion, no dialogue, just "no, only for marriage", so they girl rebelled and got pregnant at the ripe age of 10 YEARS OLD.