First paragraph: this is a typical gen.x response. No, you shouldn't work your tail off to get little to know approval. You do the job described on your contract, or in your job description, to the best of your abilities, and if bosses want to change that, they'll need to go through the appropriate bureaucratic hoops.

Aside from that, I mostly agree with you, especially your second paragraph. Another unfortunate factor may be that the female boss feels threatened by the younger assistant based on her youthful looks. Even though the assistant obviously poses no direct threat to the boss's job, she may "age" the older woman, and consequently make the boss seem like she's a step from retirement.

Shouldn't be the case, but is all too often.