Ugh, Diane Keaton was miscast (too annoying and wrinkled)
Sorry, but she's never been known for her hotness (some women just aren't sexy no matter how pretty they may be look-wise).
And while she's kept fit, she just looks like a granny who can't accept she doesn't have it anymore (and probably never did, some people like her have that "old/granny" look even when young, the ones that make you think "boy that person was NEVER young")
Not to say Jack is any better (he only got that much trim because of his fame and money, if he had neither he would have had to pay for it after hitting 40 if not earlier).
But maybe somebody like Sigourney Weaver would have been better (check out Heartbreakers to see what a red hot 51 year old SMART/INTERESTING woman actually looks like). Hell even right now she would be better (she's of the blessed few who "has it" and retains it somehow even in old age, like Monica Belluci).