I’ve always argued it’s early 20s because it’s just as close to the middle (your 25th birthday) as being 26 which is always considered your mid 20s.

Look:

20 21 22 | 23 24 | 25 26 | 27 28 29

Most people disagree with me, since they are thinking the “3” is counting from 1 to 10 but in fact you are counting from 0 to 9. Age 23 is the 4th out of 10 years of your 20s.

It just irks me people don’t understand this grade school mathematical concept, lol. You’d think they’d be smarter!

Why is 25 the ‘middle’?
There are 5 years (in your twenties) before it and only 4 years afterwards.

Of course there’s no easy way to divide 10 years into three equal groups.
So you might as well be symmetrical and say:

20-22 early
23-26 middle
27-29 late

In any case, this is not a ‘mathematical concept’.
It’s just a way of describing an age.
It’s not even shorthand, since saying “I’m 23” is quicker and more precise that saying “I’m in my mid-twenties.”

To me these terms denote a stage of your life/level of maturity more than a specific number. Generally speaking a 23 year old will be only a year or so out of college, possibly still live at home, be on his parent’s insurance, have a low-paying/entry level job, etc. In addition he’ll look pretty young. These qualities place one in their “early 20’s” regardless of their proximity to the mathematical “middle” of their 3rd decade of life.

Of course there’s a lot of grey area and these are hardly set in stone, but that’s why I usually consider 23 part of the early 20’s: at 23 I had more in common with most 21 and 22 year-olds than I did with most 24-26 year olds.

++. The whole point of a term like "mid 20’s is that you don’t know or remember the exact age.

On a sadder note, what does “middle-aged” mean? My friend laughed at me when I described myself that way; he claimed “middle-age” was the middle of the normal three-score-and-ten lifespan, i.e. 35 years old. :smack:

If you live to be 84 or so, and become an adult at about 20, that gives you 64 years of adulthood, so in the middle of your adulthood you’re about 52. Add about eight years on either side and there you go. So I guess I’m more generous than your friend but not as generous as my 70 year-old friends who want to be considered middle-age.

I do remember my mother-in-law, in her seventies, talking about neighbors or friends, and always qualifying them as “old people” or “elderly.” I was in my twenties and could only blink at her pronouncements because seventy was as old as the hills to me.