At what age you are no longer considered “young”?

I turn 30 tomorrow and it's the saddest day in my life so far. I remember when I turned 26 I felt I was old and was anxious about reaching 30 but I was happy because I still had time. I feel shitty when I think about that how dumb I was when I thought 26 is old and it tears apart. I would kill to be 26 again. Everyone says 30 is not young anymore. I cry a lot when I remember my 26th birthday, everything was still good.