Two things.
Mark time with longer references. School is a good one since it's 4 years and you likely repeated the cycle twice. Freshmen, sophomore, junior, senior. Freshmen, sophomore, junior, senior.
However short that felt for you, that's how fast the next 4 will hit you.
Now the second thing and the real reason you feel the way you feel.
Youth is forever refreshing. Someone will always replace you. And you just got done being replaced. You aged out of that 22-26 bracket. Welcome freshmen to the 26-30 league.
Better grow the fuck up and stop feeling sorry for yourself, kid. You've only got 4 years before you start feeling the next growing pains, the one about success. And how success is always intangible, how everyone else is better off than you.
That one was a doozie.