Short answer: At the start of the twenties, you mourn your teens. At the back end of the twenties, you see the thirties forming ahead of you. In the mid-twenties, responsibilities overwhelm you.

Longer and shittier answer: At the beginning of the twenties, it is a psychological self-defense against the inevitable and ongoing process that begins at twenty — called aging — that hurts the most the first time it hits, because that’s when it’s completely unknown to you and it catches you unprepared.

I was feeling my oldest around 20, 21, 22.

You still vividly remember your careless days of teenage summer. You still compare yourself with that younger version you used to be at sweet sixteen, seventeen, eighteen, nineteen. Partying without hangovers, skin with no wrinkles, superfast metabolism.

You hate comparing the teenage pics with the ones from your twenties. Because you’ll see yourself so aged. That youthful glow you used to have wilts down every year since 20, and past 25, it’s gone!

Another part of the reason is, you’re actually still quite young, therefore you don’t really know what it feels like to be really old, thus you use the description rather carelessly and you just can’t appreciate what a breeze 21 is, as you don’t know how bad 35 or 40 feels.

Around 22–23, you let your teenage ideals go fuck themselves and start to compare yourself with older people. In other words, you start to compromise. And you begin to see yourself as relatively young again. It all ends whenever you find yourself around teenagers of course, but generally, you feel good. At least about your age. Your life is full of new responsibilities though. And you can’t relate to teenagers anymore. They can’t relate to you either. They treat you like an old person and you treat them like kids.

After 26, aging accelerates, time runs way faster, and you can see thirty on the horizon. So you’re feeling old again, albeit for different reasons.