I think one big one is when you stop putting "and a half" at the end of your age. When does that stop? Sevenish? I can't think of the last time I heard someone say that they were "thirty-six and a half". If ever.
Though I might start.
And I remember a very wise teacher once told me that "once a kid loses all his baby teeth, he ain't cute anymore". Apparently, precociousness turning into obnoxiousness has something to do with the size of your incisors.
Getting ID'ed for cigarettes or drinks is another one. Can you remember when people stopped asking? What exactly was it that triggered that reaction of, "Oh, they're old enough for sure"?
But this past week brought another one. I was talking to someone a few decades older than me and I mentioned that "old age was getting to me".
The reaction I got? "Tell me about it."
"Tell me about it". Not some patronizing "Oh, you've still got some years" or "That's silly! You're still young".
Nope. "Tell me about it". Like we were peers in some kind of irrelevant segment of a marketing demographic. Like we were both members of some senior's club and we were commiserating. Like we "got" each other.
Ugh. What gave me away? You can't *smell* Metamucil and Centrum on someone's breath, can you?