With DS back at 6 months (he was sleeping 10 hour stretches as a 3 month old, although that was short-lived). With DD not until she was a year. She also had at least one night feed and just a week or two before her first birthday she STTN for 2-3 days in a row, and within a week or two AF had started.
The bfing hormone suppresses ovulation, but only if it is at high enough levels non-stop. So, if you regularly feed at night, your AF is likely to stay away longer as you keep the hormone level higher round the clock.
I saw a post on a different forum of a woman who had gone 10 years with out AF, having had (I think) 3 children in that time period as she bf and co-slept and the constant nightfeeding of co-sleeping kept AF away, but as soon as she did ovulate, she'd get pregnant before it could create an AF!