‘Die before you die’ appears in Zen, Sufi and Christian writings. Modern day writers like Kabat-Zinn and Tolle also make the recommendation. The meaning is to let go of the you created by your mind/ego before you have to.
You ego/ mind creates expectations, a self image and attachment to things. It sees appearance as important as well as anything that makes us feel separate from or superior to others. It likes wanting more than having.
You can let these thoughts go if you are fully present and conscious. Once you are aware of these thoughts as only thoughts , they lose their hold on you. For example, once you accept that you are ageing rather than denying or resisting, you die to the idea that you shouldn’t be ageing or that it is not completely natural.
So try letting go of expectations, hoping for a better past, always wanting more and living in the past. Your ego does like to define you by what you did in the past. Be where you are, here and now. You can only enjoy yourself in the present.
Try dying before you die and see if mortality loses some of its sting. Less fear in your life is a good thing, don’t you think?
Deal with reality and what is rather than what should be. You only create stress for yourself by wanting reality to be different.