Marking Time by Age or Calendar Year

Normally, I don't mark time by my age and birthdays...but yesterday's was a big deal because I turned 65, which seems to be a major dividing line in how my society separates people, depending on what side of that magic number they're on.  Aside from all the questions about signing up for the various Medicare plans, there has recently been a major distinction regarding vaccinations between those below or beyond the 65 year threshold.  Even before the Covid vaccine first came out several months ago, there was a special, fortified flu vaccine designed to protect the elderly...starting with those age 65 or above.  Now the booster shots for Covid are currently unavailable to the general population age 64 and below...a group to which I belonged just two days ago.  I plan to get both of these shots in the next few days, although I don't enjoy being stuck with a needle anymore than anyone else.  As for my opening comment about marking time, after I began elementary school I was primarily noting the passage of years by either my grade or the calendar year, not so much my age...although attaining 18 was significant as I was then eligible to vote.  As for the military draft, I miraculously managed to fall within the exact time period of President Nixon abolishing it and Jimmy Carter reinstituting registration...so my age didn't mean as much with that as it would were I just a few years older and concerned about being drafted for Vietnam. I now wonder whether I'm going to start thinking more of my physical age as a year marker now that I've passed the 65-year hurdle...