To get a bang out of something... To get a kick out of something... To get a thrill out of something... To get some excitement out of something... "half-assed" is a deliberate mispronunciation of the word haphazard (which is actually pronounced hap-hazard and NOT haffazard) Haphazard means to do something without any real effort.

To "get a bang out of" something means to really enjoy it. It's a somewhat dated expression, not really used that much anymore. In context I would say it means the enjoyed life, (but in a half-assed way of course).

to be half-assed about something = to make only half an effort to do something Think about getting only half an ass of your chair to do some work. More: I couldn't be assed about it. = I couldn't be bothered to do it. He's only half assed. = He's only half willing.

"They got a bang out of things" says that they enjoyed things in life, perhaps in a slightly humorous or boisterous manner. "In a halfassed way, of course" seems to be a reference to their advanced ages -- how boisterous can a 70+ year old person be?