It depends on the talk about exes. I had a date where he kept talking about his girlfriend who had died of cancer (I afterwards suggested that he needed to take more time to get over his grief,) and also, all the terrible dates he'd been on, which I did not point out had one common factor, and it wasn't the women, though I didn't point this out...
I don't initiate these discussions on a date, but it's quite common to talk about how you're finding the dating app - men and women tend to have quite different experiences, as men will swipe on loads, and women are much more picky. I tend to be quite vague, "I've had a few dates, met some nice guys, but they haven't worked out for whatever reason," because obviously no one wants to hear, "You're not as good as this guy I met last month, but he didn't want me, so here I am..." nor, "you're the only one I matched with, so I thought desperate as i am..."
I'm in my 50s, so it does sometimes come up, were you ever married, do you have kids? Most people will have had past relationships by this age, and if there's no history, that would seem odd. I would expect them to speak respectfully about any ex. Talk of psycho exes or how they were totally shafted in the divorce is a red flag. If they have children, I would want to know they're involved and in touch with them. By our age, the children may be adults but I would still expect them to have contact.
I am still in contact with, and on good terms with, some exes - they're just friends these days, and conversation is usually about work/parents/ children, it's just we happened to sleep together once. Anyone who isn't okay with that isn't for me, though I'd probably just talk about them as a friend initially, so they wouldn't know. Some people aren't comfortable with those who stay in touch (unless it's out of necessity because of shared children,) which is also okay, but not me. OTOH, if they'd just broken up 2 months ago, and were texting, "I miss you," that would be an issue.
In most cases, it's clear if they're still hung up on an ex, or were the reason for the break-up, and that's all useful to know. I think it's natural for there to be interest in people's past to some extent and it can tell you a lot about what they're like when they talk about it. If it's something they are too focussed on, don't show respect for those past partners, it's a reason to avoid them.