I also have noticed this trend. Most of my old friends are now fat with 3.5 kids hateing life.
I think thats a big factor, not having kids keeps you young.
An old friend i used to tear up the desert with, broke down his bike to rebuild it, had a kid, and its been sitting disasembled for 8 or so years. Hes now a fat fuck who i never see cause we have absolutly nothing in common anymore.
He works to survive and have his 6 pack every night, trying to escape from the reality he created. Sad.
Meanwhile my wife and i been married 10 years, no kids, have great carrers and just moved, just for the heluva it.
Living the dream.