My son co-slept with me till he was 9 1/2 and my boyfriend at the time who I was pregnant by (who never was at my house) wanted me to stop. I knew it wasn't a big deal for my son because he slept in his own bed at his father's. I LIKE co-sleeping! Personally, I would have drawn the line at 10, anyway, and now that my son is 12 and in puberty, it would seem creepy to me to snuggle with him at night--but that's just me. And I still hug and snuggle with him when he'll let me (he doesn't like it), just not in bed. My older daughter slept in the top bunk from the time she was about 8 and my son was 7, as the bottom bunk (futon) got too crowded.
My 27 month old daugther is still night nursing and i am in no hurry to rush her out of bed, but her Dad wants to know when she'll start sleeping alone. She sleeps in his king-sized bed and he sleeps on a twin mattress beside her on the one night a week he has her overnight.
My older kids are both honor students, well-adjusted, happy and healthy.
My son, being younger was a little more clingy than his older sister and had a habit of holding my hair as a securithy object. He wasn't quite ready to sleep alone at 9 1/2, but he was okay. I imagine he would have soon afterward decided to sleep by himself, anyway. Huge changes take place between age 9 and age 12.