I would wonder if his vision isn't good enough anymore. Has he had an eye exam recently?

Yes to keep an eye on it. Also, you don't see him as often as your mother. My siblings gaslighted me because they just did not see our dad as often. They were shocked when a brainscan showed it was clear as day he has erosion. They said it must have been a sudden decline. It was NOT.

Yes, old people lose their filter and act a tad off, but having been through dementia with parents/inlaws there is a prodromal period where those who aren't around them as much insist it's just normal aging stuff and those who are around the person a lot insist it is concerning and normal aging.

I'd say continue to keep an eye on it, because it could go either way based on the limited anecdotal information provided. In my own anecdotal experience, I've seen it go both ways in people I've known. On the one hand, it is totally normal to lose some inhibition and care less about things like using the wrong bathroom. On the other hand, if it gets more severe, it could certainly be a sign of dementia or another cognitive issue. For example, my boss is 74 and works successfully full-time but has occasional moments like what you've described every couple of months. On the other hand, my mom is 75 and declined from slipping on words here and there to being in hospice care with dementia within 8 months. FWIW, my mom's decline was very obvious to me before it was to others in her life, so I'd trust your intuition.

OP, it sounds pretty ordinary for 75. I'm in my 60's. Took care of elders who lived into their 90's. Old people can be embarrassing. lose their filter, talk too loud and be inappropriate re: hurting feelings. Hope they aren't sarcastic. Sarcasm doesn't look good as we age. OP, imo what anyone really needs to make peace with is: this is how he is now. Too much worrying about what be might in the future, reading the future, though it seems like it would be responsible, instead it's unknown. Love him for who he is right now. That's all you know.

Wondering if this is just typical signs of aging or if it’s more serious.

My 75yo father is very sharp, smart, remembers things you told him five minutes ago, yesterday, remembers things from decades ago. But he does what my mother calls “silly things”, and I noticed it for the first time yesterday.

Took him out to McDonalds for a coffee and Big Mac, one of his weekly routines. Only we went to a different McDonalds than he usually visits. He went to use the restroom and accidentally used the women’s. He didn’t notice it wasn’t set up like a men’s and went about his business, I guess. Thankfully it was empty but a woman was entering when he was exiting. When he got back to the table, he told me he’s just used to going to the left, so he went to the left without looking. I guess at the McD’s he typically haunts, men’s is to the left.

Also, NO filter. He’s not loud about it but it’s like, wow dad! Also, easily angered in public, like Ove from the book/movie.

My mom worries he’s sinking into a cognitive issue, but to me it seems typical. But then again I don’t have to live with him and deal with this daily.