Where on earth did you get that his dad thinks he's being selfish by not having kids (yet)? I can see where people who say you are being selfish probably have an ulterior motive, but it seems like it's not clear here. For the record, I support anyone being childless for any reason, but as a parent of an adult child, I get the yearning for grandchildren. My daughter knows I'd love some, but that I will respect her choice as to if, when, how, and how many. That said, if my wish ever comes across as thinking she's just being selfish, it will NOT be because I don't have a pretty epic life. I have a great income, with room for travel, adventure, dining, and expensive hobbies. I have lots of friends from my travels. I have time to spend how I please. AND I have this amazing young lady I helped make, her wonderful boyfriend, and their delightful friend circle in my life.
Tl;dr: you might be projecting a bit of a narrative there, as well as a false dichotomy that you are either child free or life sucks. Enjoy your life, but don't assume we're all missing out by making different choices.