An older friend conveyed to me pretty much the exact same thing you are, that he cannot imagine having kids at 40 because you will not be able to keep up with them energy wise. You get old and your body really starts to give in.
Alright Geoff, thanks, but you are 54 and do zero exercise, have a diet of eating out at fast food and fast casual restaurants, a body type that would be described as "meatball", and a list of medical conditions which all scream lifestyle change.
Meanwhile at trail running meets, I bump into 60 year olds still giving some 35 year olds a run for their money.