I remember getting really upset when people would tell me as I went off to college that the next four years would be the best of my life. Really? You mean it's all downhill after graduation? That seemed like a depressing perspective.
I decided to prove them wrong. Sure, college would be great, by there was no reason why post-graduate life couldn't be even better. I'd yet have new adventures, more freedom, and different responsibilities. Plus I wouldn't have to go to class anymore.
Since then, I've become determined for each period in life to be the best one yet. Sure, there are drawbacks to all of life's phases, but there are also benefits that can easily be overlooked. Even during this past year while I was coping with a hand injury, I found comfort knowing that the difficulty was teaching me to practice smarter, be prudent, and truly appreciate the ability to play the piano pain-free (though it still wasn't much fun).
It boils down to finding joy in the present. The past might have been great and the future promising, but appreciate how each moment builds on what's already happened and leads to what's next. You might find that you're having the time of your life.