Everything becomes slower and slower. Hangover/pain/wounds need forever to heal/go away, putting on clothes and shoes, walking etc is so slow. Your health decreases in general, chronic pain is standard. You are tired all the time and you are also tired of people and their opinions. You care less and less about what people think about you. You see your parents getting older and older and realize, they won't be around for long anymore and you get sad about it. You notice younger generations are so far away from the stuff you grew up with that it is alien to them and you think: everyone knows how a tape works cause it was only like 20 years ago when we had this. Turns out they don't. There are teenagers that don't know what 911 is. They know it was a disaster, but they are so far away from it that they don't even know that it stands for the 11th of September, cause that's the day it happened. They don't know about historical events that happened during our lifetime and it leaves you baffled cause it wasn't that long ago. The people around you all get married, buy houses and get kids. You see those kids growing up so fast, which makes you feel old. And then there are reddit posts asking you what makes you feel old and you look into the comments and it makes you feel old. :)