The only reason I mentioned that "баба" could also be younger than her husband was to highlight that "баба" is probably just "a spouse" and not "a grandma" as the original translation suggests. Maybe, she didn't have children in the first place, let alone the grandchildren. Also, the fact that nobody except for the mouse was there to help the old couple to break the egg kind of implies they lived alone.
Btw, I'm kind of surprised what does the weight of "баба" have to do with the activity of breaking the eggshell?
The tale IMHO is about how the extraordinary does not belong in the ordinary. In an ordinary place two ordinary people who had an ordinary hen all of a sudden got an extraordinary thing - a golden egg. Being a perfectly ordinary, all they could use the golden egg for was to break the shell and fry the internals - they could find no other use to it. But their attempts to fit the extraordinary into the ordinary failed. So, eventually the egg fell down and became spoiled to be eaten. (But the most outstanding part - the golden eggshell - was still usable!) The ordinary people began to cry for they cannot get out of their cognitive box to realize the potential and the proper use of the extraordinary that they encounter. So, could they reflect on what happened and educate themselves and elevate their consciousness? No, that would be impossible for the ordinary, don't bother, stay where you are, forget the golden egg, we'll get you another perfectly ordinary egg you could use. Only then you'll be happy. No moving forward. End of story.