I would hope at the age of 42 you've thought your politics through to the extent that you won't be throwing your support behind the Dems in 15 years...on ideological issues of that import, by the time someone is in their 40s I'd expect them to have clarified the issue in their own mind. If not, that's an indication of muddled thinking, and certainly not someone I'd want on the SCOTUS.
At my age, I believe I have put a lot of careful thought into my beliefs and have a strong foundation for such thought.
Of course, I probably thought the same 15 years ago! I can promise you, I have changed!
Many experiences can bring about profound changes in one's thinking, and a lot can happen in then next 20 years.
As I have a foundation that doesn't change, the Bible, my fundamental beliefs and underlying principles aren't likely to change. But the circumstances around me are constantly changing, so how I apply those principles in my life may very well change in the next 20 years.
Look at all the FReepers threatening to change party affiliation at this one "last straw" event.
I'm not saying her background is irrelevant. I'm simply saying that to insist that opinions should be stable by age 40 is a bit arbitrary. The words senator and senile both have the latin root senex, meaning old man or elder, as it was deemed that older people have the wisdom to govern. By the 60s or 70s, yes, the concrete has probably set. In the 40s, the concrete may not be soupy, but it's not dry, either!
In addition to one's background and the decisions one made in youth (or middle age), you should look at the direction of the person's life as a whole. Can you see a pattern of growth or maturity? Is the direction acceptable? Are we looking at someone who flip-flops constantly with no direction, blown by the winds, or someone making a steady progression in a good direction? What is the foundation on which they stand?
Having said all this, I'm STILL not thrilled by this appointment. I guess we'll all see.