Hillary Clinton was also raised in a politically-conservative household, without much exposure to any other viewpoints; she was 13 when she was canvassing for Goldwater. Keep in mind that when she got to Wellesley college in 1965, she was still in that mindset; she joined the campus Young Republicans when she showed up on campus. Yet by 1968, she had gone from Republican to moderate Republican to deciding the Republicans were a) wrong, and b) racist, and that she wanted nothing more to do with them.
Sanders is older than Clinton; in 1962, he was in his early 20′s, and so already had a chance to form—and start acting on—his own beliefs in a way that many 13-year-olds have not.
If you count both track records from their early 20′s, then you have to include a young Clinton walking out on the Republicans in 1968 on the grounds they weren’t doing enough for civil rights.
Now, I vastly prefer Sanders as a Democractic candidate, personally. But still, let’s be fair to Clinton here. I think in many ways it counts for a lot that, having been raised staunchly conservative, once Clinton was out on her own and exposed to a wider range of viewpoints, she re-examined her beliefs, found them lacking, and changed how she acted.
(Still going to vote Sanders if given the option, though.)