People born after the year 2000, who are now adults or close enough to adults, make me feel old. I mean that feels just like last week.
When your kids are growing up and they start saying "wow, I feel like time is going faster now". Like I haven't noticed that yet?
When people start talking about things that are going to be completed in the year 2040, or that are going to happen within the next 25 years. I will be lucky if I'm still alive and have most of my marbles then.