As you may be aware, CC, hot flashes most commonly begin during perimenopause, before the last period.  However, there is wide variability in the symptom profile that women present and, in my practice, I have seen many, many variations on what we consider the norm.  So, yes, you could be starting menopausal hot flashes at this stage in postmenopause.  Hot flashes are a function of estrogen lack.  We can store a lot of estrogen in the fat cells and how long it takes you use that all up will impact on symptom occurrence and severity.

You asked how long hot flashes can last.  Unfortunately, we see women who never get over hot flashes.  Usually they will fade significantly by the early 60s if not before, but it's reported that 15-20% of women will always have them.  I have at least 5 women in my practice in their 80s who have proved to me that this is true.  Doesn't seem quite fair!

Because what you are experiencing is somewhat unusual, CC, it is important that you rule out any other cause for hot flashes.  The one that springs to mind is low thyroid which causes many symptoms which are similar to those in menopause.  I would strongly suggest you see your primary care doctor and have a simple blood test that can rule out thyroid disease and do any other testing that she/he thinks is appropriate.

Good luck to you, Sandy