Time flies it really does

I'm in my early 30. I've only lived 30 years but why do I feel like I've lived forever and I've already felt all the emotion that human could ever feel? And one of the biggest mysteries of my life is why I stopped being happy when I was 20, lol Is it just me or anyone else who kinda feel like this?

to be honest people told me that I'm still young and there's so many things I can do. but from time to time, regrets collect like old friends. at this point It's like there's big pond of regrets in my heart and I know it won't go away until I lie cold and rotting in the bitter earth :/ 

when I was younger It was way different. my mind was like river so I could let go of anything as the river flows, I meant if I wanted, literally anything any thoughts or feelings. But I don't know since when it became impossible to let go of certain kinds of emotions. They're always there in my heart and have become a part of me. :/