I'll speak as someone that waited until almost 40 to have kids and who feels, in hindsight, I was being completely selfish. I prioritized my career, my travel, my sleeping in, my social life, my leisure, etc. As soon as you become a parent, you realize you shorted yourself and your kid shared time on earth together. I also just don't have the energy or physical ability to play like I would have at a younger age. It's not something you can really grapple with or consider the magnitude of as a childless person purposely avoiding/delaying it. I don't think it's necessarily intentionally selfish in the moment, as you're living it, but later sometimes you get to reflect back and see your decisions as what they really where with the clarity of hindsight and you'll understand what you really did. It's a weird thing that happens and I think part of the whole "wisdom with age" thing. I think I was just being selfish. All the travel and me stuff I did in my 20s-30s is not really very important, my identity as a parent to the humans I created is my identity now, It's the only part of my identity I really care very much about. Sure I still have hobbies and travel and stuff but it's on an entirely different plane of importance.