To me, the biggest hitch in a 59-year-old Walter is that his younger sister, Beneatha, needs money for her education.
So... that'd be a 40-something year gap between siblings? Even if Denzel, as dramamama rightly points out, plays younger than he is (and he usually does), a 40-something Walter still has about 20 years on Beneatha if she's at the end of her school-age-appropriate casting.
They'll still very likely do a good job with the material outside of that age objection, and the production will roll in the dough, and really that's the bottom line. Does it bother me? Sight unseen, yes. Will it bother me during the show? Hopefully not, though if the production is flat and dead than it will be difficult to ignore. Has it happened before and will it happen again? As safe a bet as there is while there are still bankable stars and roles they want to play, age recommendation be damned.
Words don't deserve that kind of malarkey. They're innocent, neutral, precise, standing for this, describing that, meaning the other, so if you look after them you can build bridges across incomprehension and chaos. But when they get their corners knocked off, they're no good anymore…I don't think writers are sacred, but words are. They deserve respect. If you get the right ones in the right order, you can nudge the world a little.