With ds#3, ds#2 was 17 months old, caught the first PP eggie.
With dc#4, ds#3 was 22 months old, caught the first PP eggie.
We weren't actively trying, but we weren't preventing, either. We knew that our chances were reasonable because of the ages of our kiddos, and we wanted more, but weren't trying to "plan" them, if that makes sense.
With ds#2, ds#1 was 26 months old, and I had one cycle (ovulatory) before the cycle we conceived. We were actively trying.
I have heard/read that the longer it takes for your cycles to return, the more likely you are to release an egg before bleeding (as opposed to having an annovulatory cycle/bleeding first). I obviously react strongly to the presence of breastfeeding hormones in my system.
Oh, and I always have really intense, crazy dreams in the 2ww, which is my only clue/symptom until ms sets in around 6 weeks. I've always tested early because of the crazy dreams.