Today could be one of those boring ol' happy days I might one day randomly reminisce about in the future.
Sometimes my brain hits me with the most mundane memories, and even those bring comfort & nostalgia at times. Trying to appreciate all the little things and enjoy the moment.
Friend, you're 20. The concept of "potential" being "wasted" at this point in your life is non existent. You're still right at the start of the journey. Don't dwell on what you think you might have missed yesterday. Make a plan for tomorrow.
Due to my mental illness, I'm never really very happy or very sad. I live in a state of general contentment though, which for me is preferable to experiencing either extreme.
A gift I've received from years of spiritual/psychological work and exploring has been the ability to, every once in a great while, experience and create beauty while it happens. It's so much more pure than that vague sense of loss that comes with reminiscing.