I have nostalgia problems. Sometimes I feel like all I do is think about what was and what could have been. But all of that is a waste of time. There's no such thing as time travel, and you can't ever go back. If you live your entire life looking back on the past, eventually you'll reach the point that when you look back, there's nothing to see.
We need to accept the phases of our lives as they come. You can't change what happened yesterday, but you CAN change what happens today. Embrace the fact that you're growing up. Make the best of every phase of your life because they all have something good to offer.
"I think people need to realize I'm not changing, I'm just getting older. . . I'm just growing up." --Justin Bieber