The perception that our friends seem to stay the same age as we get older can be attributed to a psychological phenomenon known as "perceptual stability." There are a few factors at play here:
Shared memories and experiences: As we age, we tend to maintain friendships with people we have known for a long time. These long-standing friendships are built on a foundation of shared memories and experiences from the past. When we interact with these friends, it often triggers memories of our shared history, making it feel like they haven't aged much since the last significant memory we have of them.
Gradual changes: Although our friends are indeed aging, the changes that occur over shorter periods might be less noticeable. The aging process is gradual, and we may not perceive small changes each time we see our friends, especially if the time between interactions is relatively short.
Mental models: Our minds create mental models of the people we know, and these models can become somewhat fixed over time. These mental models are based on our strongest memories of our friends, which are often from earlier stages of the friendship. As a result, when we think of our friends, our minds tend to go back to those earlier memories, reinforcing the perception that they haven't aged much.
Self-perception: Another factor that influences this phenomenon is our self-perception. As we age, we often feel like we're staying relatively the same, even though the outside world might perceive us differently. This cognitive bias can extend to how we view our friends as well, assuming they are staying the same while we are changing.
It's essential to recognize that this perceptual stability is a subjective experience and can vary from person to person and from one friendship to another. Some friends may appear to age more noticeably to us due to certain life events or changes that are evident, while others may seem to remain unchanged.
However, as time goes on, the cumulative effects of aging become more evident, and the perceptual stability might start to wane. Major life events, such as milestone birthdays or significant physical changes, can also challenge this perception and make us more aware of the aging process in ourselves and our friends.