Get in touch with your essence to find out what you came here to do, or what will most fulfill you now that you are here. Youth, in this sense, is mostly metaphorical. It means that which is of your essence, your birthright, as compared to that which is imposed upon you by circumstance. Reclaiming the promise of your youth is a core task whether you are young, old or in between. The promise is that which you will remember well on your deathbed, the mission implicit in your soul. When I am fulfilling my promise, I feel a depth of well being, but when I neglect it, even for short periods of time, I am consumed by anxiety. Anxiety can sometimes be helpful as the spiritual version of pain. Just as bodily pain is crucial to keep you from harming yourself, anxiety and depression are sometimes crucial in telling you that you have "departed from the experience of meaning" (the Eranos I Ching) and need to move toward the experience of meaning, toward that which is intrinsically significant. This is easier said that done as we live in an extrinsic world that makes constant demands on our attention, time, energy and resources.
To ground this in practicality — is there a "big dream" you've had but are now neglecting? If the big dream is truly connected to your promise, you need to fulfill it. A good rule of thumb for fulfilling your big dream is that, at a minimum, any big dream needs at least two hours of focused work every day. Two-hour-plus blocks of time are hard to find. My answer is to get up early in the morning and do the high-value work before the distractions of the day set in and the low-value mechanical tasks take over. The big dream is not necessarily a creative or artistic task, it could be anything that fulfills your soul — friendship, raising children, gardening — only you know what your big dreams are.
Consider this a propitious time to fulfill the promise of your youth.