If you're just talking about old enough to have a grandchild, 50 is plenty old -- indeed, old enough to have gotten married after college, had a kid who got mar

If you're just talking about old enough to have a grandchild, 50 is plenty old -- indeed, old enough to have gotten married after college, had a kid who got married after college, and that kid now has a kid of their own. At least one of my high school classmates did that. (I'm 51.) If you're talking old enough to be, say, a college student's grandma, then obviously your 70-90 estimate is much more likely. (Bigger picture: I've been professionally programming for three-and-a-half decades. I find myself more and more annoyed by the user-unfriendliness of tech as I age. As an on-topic example, earlier this month Amazon's mail-to-Kindle feature rejected an EPUB I sent it, and when I used Calibre to convert it to MOBI and sent that instead, lectured me that MOBI was obsolete. I guess this is especially annoying because it seems like they're replacing a service which basically never failed with one that is failing like 10% of the time I try to use it...)