Do I have a right to feel old at this age?Watch
Easier said than done, but you can't live in the past.
If you keep thinking you're old in your teens and early 20s; one day you'll actually be old (i.e. pension age) and think how silly you were thinking you were old before you even started living your life.
Embrace your 20s, it's the best decade of your life. Live in the present.