Hi, lately it seems as though there's barely enough hot water to take a
shower. I went downstairs to observe the hot water heater...

-There's no sign that the water heater has 'blown up' like seems to happen
whenever my dad's water heater expires
-The heater has the date 1990 on it, which I presume to be it's installation
date.
-The heater is natural gas. I didn't notice any smell...
-The heater was warm to the touch
-It hasn't been very cold here lately.

Do these things just fade away? Or do they always go out with a bang? How
do I assess the situation?

Thanks
Steve