> I also get nostalgic at times about the wonders of youth, experiencing things for the first time
Yeah, I guess at one point I'll feel like that too perhaps, but I still feel young, I feel like I have more energy each day than the previous one, and every month is experiencing new things for the first time, and personally I don't want that to stop and experiencing those things through the eyes of my children, I want to continue having those experiences myself, together with my wife :) I guess that's where the offhand "I'm selfish" sentiment from my previous comment comes from.
> If I do nothing else in my life, I would still feel immensely fulfilled.
Do you think you'd feel fulfilled if you didn't have children? Maybe this is the core differences, I feel fulfilled in my life already, more than ever and more every day, I live exactly the life I want today, and I wouldn't want to change it for anything. Even if I became deadly sick tomorrow, I'd feel fulfilled by the life I have lived.
As I approached 30 I felt what I now understand as anxiety. Nothing crazy but you wake up one day, you're a year old, you take stock of your life and see what you've accomplished. I chased credentials and new jobs, did well but not yet able to retire. Old relationships grew strained and new ones are hard to form. Etc. I was definitely more afraid of death than you are.
I stumbled into children. Met my wife, didn't overthink things and decided to marry her after several years of courtship. She wanted children so I went along with it.
After they were born, the anxiety went away entirely. I just watch them grow older. It might change after their grown but hopefully they'll have children and I'll be able to repeat the process (my parents sure have).
To answer your question, I don't see a way I could have been fulfilled without children. It brings a lot with it as well. Before children the worst thing that could happen to me is dying. After kids you realize there's a whole world of potential pain and sorrow that is now before you. You're also constantly reminded that every kid is a roll of the dice when you see others in a similar spot as you have children with health or behavioral issues. It's terrifying.
But for me life shouldn't be all pleasure. I've always liked exercise because it does feel terrible while you're doing it. But at least you're doing something. I feel that way about children.