I'm in my twenties. Sometimes I forget my age. Only ever by one year -- I just don't remember if my birthday passed or not. Kind of like in January when write oit today's date and accidentally use the previous year. After a few mistakes, your brain adjusts and you start using the right one. Same thing for my age, except that I don't actually think about my age very often; it hasn't mattered much since I passed 21.

A colleague of a old friend would recall your birth year (and date?) to know your age. It is a value about you that doesn’t change and then you can derive the age.

I’ve started doing similar now. I don’t often recall my age or the number of years my wife and I have been married, or, heck, even our kid’s ages. But I recall all the years and dates. In this way, I more easily appear to recall the right value.

I'm in my late twenties and sometimes I need to pause, a bit like dealing with left/right or east/west.

I may forget my age, but I can't forget I'm now over 30.

I've no idea of my precise age.

Of course. The Uncertainty Principle encodes this consequence: we know exactly how fast we are aging, ergo we cannot know exactly how old we are.