Only the position is locked. It is possible to lock different aspects of any layer, i.e. lock the transparency (this means transparent pixels remain transparent regardless of what you do to the non-transparent pixels), or lock the image pixels (the reverse of the former), or lock the position, or lock the whole layer.The background layer in PS is locked by default.
I to am aging (63) , this is a hobby . I drag a photo into my dock to open PS . When it opens an image appears , layers box has one layer (background). Out of curiosity I used my pencil to trace the image in black (it works) . Later on the photo will become a line drawing that will be printed off , enlarged with a projector then airbrushed into a finished painting . I have been at Ps for four years now and still confused . Thanks
The second way is to double click the background and rename it. This removes the lock, but you have to be careful to save it under a different name in case you don't like your work.