Often times you'll see that there are negative views on immortality, that it's against nature, the natural process of life, that you'll see all your loved ones die, and always have a hole inside of you. That you'll just end up as a cold person wishing for death to swallow you whole.
But what if...
Hypothetically, if you became immortal, there would be more to life than loving other people, if you put love aside there is a whole new aspect to living thousands of years that you'd see.
Now imagine living to see the first planets colonized, seeing our first contact with Aliens, seeing if your favourite cricket team will ever rule like the Aussies or West Indies one did, heck if cricket is even alive, seeing new technology, progresses in medicine.
And from there my fear takes over. I do not want to die because I want to experience all of those things. None of us will ever get to experience those things.
As a wise man once said: "we were born too late to explore the Earth, and too early to explore space"
The examples you gave all put me in a mere spectator position. A passive bystander cheering on as things around him unfold. It didn't convince me to long for immortality.
Instead of longing for immortality just so that I might witness all the great achievements of mankind, I would rather do something productive to the best of my capabilities that might help humanity to progress in whatever field I am working in, no matter how minuscule my contributions might be.
You are fascinated by space travel and space in general? Me too. Unlike you I am not at all saddened by the fact that I might not get to witness the colonizing of Mars, even though I am pretty young and who knows perhaps I might end up buying a property on Mars in next 20 years. Still I am not all too hyped up about the end goal.
Who am I kidding? I would love to shake an Aliens hand, if they have one. But instead of getting depressed over missing out on the good stuff I am more focused on understanding the way we might get to the end goal.
Instead of hoping to witness us colonizing other planets, I try to look up at the current progress and read about it. I try to understand why it is taking so long and what issues are holding us back. Instead of hoping for the end goal I focus on the process and find it much more fulfilling.
I am not an expert on space or anything but just reading about it, thinking about it and trying to come up with my own answers to the problems in what ever way I can, gives me so much satisfaction that I don't care about immortality. I don't care about missing out on first alien contact.
That's what I would suggest you, just focus on the process. See the beauty of it. Try to be part of the process in whatever way you can. Think harder, ask and answer. We are lucky. It's the century of information sharing. All the current information of humanity is just a few finger tips away. There is no secret which only a handful of the privileged have access to. It doesn't even have to be a formal scientific book. Just look up some YouTube videos on the matter. Let the mysteries and challenges of the journey fascinate you. Quantum mechanics, artificial intelligence, robotics there is so much going on to think about and try to make sense of it. So many issues to resolve.
Enjoy the journey for the journey is always much more enjoyable then arriving at the destination.
We the modern people would not have been able to build spacecrafts without the help and selfless contributions of the ancient people. Hence for me it's so beautiful to know and realize that the fruits of our labour might not be ready to harvest in our life time. Just like we could enjoy the fruit of generation before us likewise the seed we are sowing now, the fields we are planting today, their fruits aren't ours to eat, it's for those who will come after us and it's beautiful the way it is. We can't just enjoy the riches of those before us and contribute nothing, we must too leave some riches for those who are to come after us.
There is no need to be depressed, change your perspective and enjoy the journey or you would miss out on the fun part. Existence in itself is beautiful, life on its own is fascinating enough and we don't have to experience all the great things to feel amazing. The time we are living now is the best time.
If we were born earlier at time when there was still much to be discovered on Earth. We would have been most probably some peasants working for some privileged landlord who hadn't seen anything outside of our town and died an early death. It would not have been some fantasy world where we all would have been some adventurers setting sail to any part of the world and discover the earth.
For me the glass is always half full and I am content with it.