1. When and how did you first become aware of death, and/or that you would one day die?
2. When did you start having existential crises/depression, particularly any related to the "meaninglessness" resulting from life's finiteness?
1. Since always and never at the same time. Since age 4 I don't believe in Heaven, and I was the spokesperson of death: "what do you want to do before you die?/how many years do you think you'll live? Why the hell would you want to be immortal?", and such. Two grandparents died, and I just shrugged it off. They were old, it was expected. I realized my first grandfather (the one I had more contact with) had died like 3 years after, when I got stuck in an elevator with an old man who had the same fragrance as my grandpa. Only then (and only that moment) I missed him. It struck harder when a friend from my childhood who I hadn't seen/heard of in years commited suicide, because it was like the realization that someone young is not there anymore kind of makes a hole in the memories, I don't know, it's like having the preview/thumbnail of someone but nt being able to access to the "archive" anymore. Anyway, I felt strange for a couple of days and then I forgot about it.
2. My existential crisis and depression aren't related at all to the meaninglessness of the finite human versus the infiniteness of the universe (it's the Romanticism core, btw). I am well aware that, to the world per se, and the universe per se, I mean nothing. I'm just here because of a natural "accident". The whole humanity can disappear, and no one will care or miss us. The entire planet can disappear and no one will care. Outside the atmosphere there's complete silence. I'm fine with that. In fact, I find it fascinating. I'm just enjoying my five senses and my ability to think in a world that in a couple billion years will no longer exist, learning things that will only go with me to the grave... to be honest, for me meaninglessness is freeing. I always think what a fool I'd be if instead of seizing the opportunity to see and learn and be amazed by the world that surrounds me, I was so caught up trying to figure out my "purpose" or destiny or being sad because I'll no longer be alive in a couple dozen years that I'd waste my time.
Of course, human things happen to humans because of the "humanity" (as in social construct, artificial world, culture, whatever) we developed, so all of that tends to come in second, covered by loads of crap that make one depressed. Fortunately for me, death or meaninglessness is not one of the reasons.