Yeah, this is not too surprising. The problem for Sanders is not necessarily just the immediate impact, but also that it's an issue that will get raised by voters/other candidates/the media/party elites if he rises in the polls again, which could limit his upside.
I'd bet that Biden isn't thrilled to have candidate age and health become more of an issue again either, though.
And, yes, I know there are no bright lines when it comes to age. But I don't put Warren in the same category as Biden/Sanders. There's a pretty big difference, in terms of life and health expectations, between a 70-year old woman and a 76- or 78- year old man.
