Come back when you've got kids and tell me all that again
When someones hitting their 40's without children, its probably not best to mention. After all, you really don't know why they might not have them.
But to your point...
Some famous names off the top of my head.
Erwan le corre has kids. David Goggins has kids. Cam Hanes has kids. Laird Hamilton has kids... the list goes on and on.
Now you may say 'but those guys are .... ' and everything that comes after that are excuses to me.
Personally i know guys in their 40s who are ripped to shreds with young and old kids. Hell, i have competed with guys who have multiple kids and are in better shape than i was at 20. They are crushing BJJ against 20 somethings as much as they are 40 somethings .. .and they are amazing Dads.
Now let me make it clear that i am talking about MY outlook. If people are happy as they are, they are happy as they are. For me I will keep pushing as hard as ever.