I recently saw a portion of the Karate Kid on TV, and I couldn’t help but think: I don’t remember all of these people being so young. Last time I saw this, I looked up to the main character. Now he seems like a child.
Obviously, it has probably been at least a decade since I’ve seen the movie. But what phenomenon is this? Why would I perceive characters so differently? How could my age factor into my perception of others?
Subconsciously, we must know our age relative to those we see. Because while we change, college kids stay the same age. What changes is us, and the people that are in college, but the age of the people in college stays the same. Therefore the change is not them, it’s us. In our perception of ourselves.
Perhaps, we always compare others to ourselves. Looking for those subtle and not-so-subtle signs of aging. And as we age, we see less of those signs in those younger than us. So as we accept the slow progression of these negative attributes of our own beauty, we cannot help but notice the lack of these attributes in those younger than us. As we accept those as part of our reality, we notice that these attributes are not part of those realities of those younger than us.

Our perception of ourselves is the zero point. Every time we look in the mirror, we are different. We change slowly over the course of our lives. We age. And we adapt to each new perception of ourselves.
You’ve heard the story of the frog being boiled alive. By slowly increasing the temperature, the frog never notices the change. I think this story closely parallels this psychological mechanism. We are not aware of the change in us, because our aging is the combination of many small changes over a long period of time.