It varies not only from person to person but from nursling to nursling. I've always been the very definition of ecological nursing, including delayed solids and non-breastmilk liquids, cosleeping (and thus nursed throughout the night) and napping with baby, never used pacifiers or other comfort objects, etc, and with the first 3 babies I got AF back at 5-6 weeks postpartum. I envied all those mamas who kept AF away with nursing!
I'm now 9 months postpartum with my 4th baby, who nurses LESS at night than any of my others (and who is still EBF), and all I've had by way of AF is one half-hearted attempt at around 6m. I'm the same weight as I was the other times, but I am older than with my others (I'm 34 now, I was 29 when I had my last baby), though, so maybe that makes a difference.
I don't necessarily WANT to get AF back, because my milk supply always goes down for the few days before I start. But I feel like my body is trying to ovulate every 2 weeks and can't quite make it, except I don't know it didn't make it until 2 weeks later when I don't start AF, and instead start trying to ovulate again. It's just strange not knowing!