I just think it's cool you have a chance to ride with your son, not having any kids myself

As others have noted, lots of fit and pain issues don't surface until you've ridden 50 or 60 miles or more. I did 34 century rides last year, and I'd say on every one of them either my feet, or my butt, or something was feeling the pain by the end, even if my aerobic system was still going strong.