I am 55 and I also went 11 months before my periods returned last year. Since then I have had a few very light ones very spaced out, and am expecting to bleed again as I have days when I feel like I might. I was regular until about 2 years ago, so I guess it explains why at 55 I am not post yet. Also my cycles were more like 35 days not 28, and I had 5 pregnancies so maybe that is a factor. Also my great gran had a baby at 49.
Perhaps you could think about your family history, previous cycles etc to see if there is a pattern. Also are you seeing signs of high oestrogen such as stretchy vaginal mucus or breast tenderness? These signs may indicate you are still making oestrogen and therefore a lining that needs to be shed, even if you are not actually ovulating.