Too Early for Alzheimer's

Yet again, somebody I have no recollection of walked up to me in the grocery store today and greeted me as if we have been acquainted for a long time. This has been happening, on average, 3-6 times a month for the past few years. Someone crosses my path and they seem to know me very well, offering personal details that a casual stranger would not know, yet I've not the slightest inkling who the heck they are. Most times they don't even look remotely familiar and often they talk about discussions we apparently had where the subject matter, wording, and focus sounds just like something I would say. Sometimes I am able to place them. The rest of the time it is a bit unnerving but at least I've gotten really good at politely faking familiarity because I don't want them to feel bad or unmemorable. I know I partied hard in my late teens but DANG!! I don't think I partied THAT hard!!!