Thus when you cast it considering the main drive of Pierre in Comet is his existential crisis, you should cast it older as it is more in line with a the contemporary "Mid Life crisis" then the crisis someone has when they turn 30, which would be truer on paper, but not in terms of authorial intent.
Culturally, you can't make those assumptions. An existential crisis of a twenty-something Russian man in the early 19th century while his country is at war is hardly in line with a contemporary American middle-aged man's mid-life crisis (not to mention, there are characters a generation older than Pierre throughout the novel). And even we pretended you could, Patinkin's still too old. But the stereotypical American mid-life crisis is usually the reverse of Pierre's circumstances. It is often associated with a desperate attempt to recapture youth rather than a quest for morality and peace.
Natasha is 13 at the beginning of the novel, but Pierre is only described as having finished his studied abroad, which means he's somewhere in the range of 18-22. Whether referencing "mid-life" or not, he's still probably only 5-10 years older than Natasha, so if you want to put a contemporary American slant on the casting, you need a Natasha who APPEARS mid 40s, at the very least, to make any sense of Patinkin's casting.
"What can you expect from a bunch of seitan worshippers?" - Reginald Tresilian