In 6th grade, "dating" generally means eating lunch together, talking on the phone at night and making funny "do you like me, check yes or no" notes. There are some kids who actually "date" in group dates at the movies. However, in 10 years, I haven't had a 6th grade relationship that was resembling anything even remotely like the 8th graders and high school students who do date. Very rarely, they will hold hands at a school dance. That's the extent of it.
My son has a girlfriend and he's in 1st grade ;-) He eats lunch with her every day, walks her to the bathroom at recess so the bigger kids aren't mean to her, buys her Christmas presents with his own money etc. She's been his "girlfriend" since they were 4 1/2. I did wonder how long this can go on when I found the two of them laying in bed together a few weeks ago... though he was reading her Calvin and Hobbes.