What does "a life impervious to skincare routine" imply by the speaker?

Question

I have some difficulty in understanding the metaphor or implication of "a life impervious to skincare routine". I could sense that the speaker is speaking about the old woman in an approving tone, but what does she actually mean? That the woman is so strong, tough, mentally and physically, and experienced, so that she did not care about the facial beauty? Why use "skincare routines" here? My guess is that "she does not use skincare because she doesn't care"?? Could anyone please help me understand, or rephrase it in a straightforward way?

In the context: 'I' was the carer of Will, a quadriplegic in wheelchair, and we were at a wedding reception, and the woman is also a guest.

Here is the sentence, and all the related context:

The elderly woman on his right turned out to be a former MP who had campaigned on the rights of the disabled, and she was one of the few people I had seen talk to Will without the slightest discomfort. When she briefly got up to leave the table, he muttered that she had once climbed Kilimanjaro. ‘I love old birds like that,’ he said. ‘I could just picture her with a mule and a pack of sandwiches. Tough as old boots.’………

………… At one point, when I started to feel properly awkward, I felt Will’s arm slide off the chair beside me, and his hand landed on my arm. I glanced up and he winked at me. I took his hand and squeezed it, grateful that he could see it. And then he moved his chair back six inches, and brought me into the conversation with Mary Rawlinson.

‘So Will tells me you’re in charge of him,’ she said. She had piercing blue eyes, and wrinkles that told of a life impervious to skincare routines.

‘I try,’ I said, glancing at him.

‘And have you always worked in this field?’

‘No. I used to . . . work in a cafe.’ I’m not sure I would have told anybody else at this wedding that fact, but Mary Rawlinson nodded approvingly.

Me Before You by Jojo Moyes

Answer 1

First of all, it's likely just an assumption on the part of the narrator. I doubt it's known if the woman in question actually has a history of having tried skincare routines.

That aside, I will rephrase the sentence:

She had piercing blue eyes, and wrinkles that indicated she was immune to the benefits of skincare routines—none of them could prevent her from showing signs of aging.

But it's not her life, literally, that's immune. Instead, the actual sentence might make more sense with some additional words:

She had piercing blue eyes, and wrinkles that told of a life spent being impervious to skincare routines.

Whether or not she is physically unable to benefit from skincare routines, or she has had other things going on in her life that have caused wrinkles more strongly than the skincare routines tried to prevent them is unknown.

Answer 2

No, I think it's all about her experiences that come with age and maturity. The meaning of the word 'impervious* is unaffected by something.

This could be a marvelous way to tell that the wrinkles on her face talked louder about what all ups and downs she had in her life than the skincare she might have opted for.