Super heroes having a life.

Why is it that in the comics and the like our Superheroes never seemed to be able to have a life. Sure things are hunky dory for a bit but then something comes along and mucks it all up. Also why do our heroes never seem to age out of their persona. Take a look at Capt America, sure the super soldier serum slowed his aging but come on there is a limit?! I am just curious as to what would happen if the comics actually explore such a thing not as an Alternate Reality or some such but in the Prime Universe, let them get married, have kids, grow old. Etc... Etc... Etc...