I'll have to ask my mum when she had her 1st ppAF now!
9 months is an early return for AF for alot of women, so it's likely that your mum would have gotten AF back around that time whether or not she weaned. It's hard to say there..
As for getting AF back around the same time each baby, it might depend upon how much they are BFing. Although with my DD, AF came back 7-9 months (can't remember exactly) and she had NO solids just booby, and this time with DS, I had a *possible* AF when he was just over 6 months. He has been eating solids since 3 1/2 months! So now I don't know lol I think all i've done here is confused myself and everyone else