What the fuck do I say/do in this situation?
Player is an old guy. He's been playing with us for years but is starting to show signs of dementia. But that's not the problem. We can solve the issues of memory by just reminding him that he can ask the other players for information and asking him to remember. But I am purposefully making memory, note-taking, and map drawing be important aspects of the game. It's part of player skill. The thing that's annoying is that he acts like because he's old that he knows more about the game than anyone else, but the reality is, most of what he knows has been gathered from "Story-games" or modernist D&D where you role play everything, and I guess past DMs handwaived everything for the player's benefit.

For example, because his character has a history of blacksmithing, he thinks that he can just make weapons without having to keep track of materials. And he treats the party's inventory cart like a black hole that he can just pull anything out of without actual inventory management. He'll say, "I want to pour holy water on this dead body!" And I'll ask if he's actually carrying holy water. I look at his character sheet, and it's not written there.

I could stop playing with this dude, but I'd rather keep him as a player. So I have to talk to him, I understand that. But where should I start? What are some things I should keep in mind about this situation when I do?