Disclosure: I’m not technically a Baby Boomer, but Gen Xers tend to get lumped in (actually that might be part of the issue).
I fully understand the term ‘OK Boomer’ started as a throwaway joke, and quickly became a meme, and initially served its purpose in replacing the eyeroll emoji in the specific circumstance where an old person said something explicitly typical of their generation that required a dismissive response.
But I think it’s evolved way beyond that now, and the usage I’m seeing could now be summarised as ‘older people are so stupid/gullible/irrelevant/laughable/predictable/whatever’ - in other words, I think it has changed from a response into a general purpose prejudice; it’s stopped being about how some stupid things seem to be more commonly uttered by older people and it’s very much more, now, about how older individuals can be expected to conform to a stereotype. A statistical correlation (which may have had a basis in truth) has been generalised into a prejudice about all of the individuals in the group.
Of course, I’m not saying the magnitude of harm done is anything like it has been for other categories of prejudice; it obviously hasn’t, but I don’t think that necessarily excuses it as right or acceptable either.
It’s possible that I am just being oversensitive and there isn’t even a problem, but to me, it seems like there is; I didn’t go looking for a reason to be offended by something; this came to me, with offence as its explicit agenda.