How to deal with constantly intruding neighbor/grandpa?

I just moved in last month. There's a grandpa under me that warned me about noise. I thought I would was just being loud so I apologized.

Last week he started to lecture me about locking my bike stand properly so it doesn't fall down.

Today he rang my doorbell and I apologized for noise thinking it was a noise issue, then he went on a tangent and rambled explaining how to wash my pants, how to dry them quickly, what to put in my washer so it's not too loud for him, what to buy so my doors don't clunk, what to do so my futon doesn't fly away when hanging etc.

It wasn't anything terrible and I'm very good at defusing people so he turned friendly, and I don't want to be overly paranoid. If anything, he probably is just lonely and excited about having a new neighbor, but I also feel uncomfortable with the idea of him randomly coming to my door and rambling for a while since I have to tell him I still have something to do before he leaves (I do get busy sometimes).

When I said goodbye and he left, two minutes later I hear my door handle being turned as if he wanted to come back in. I just played silent in my apartment till be went back downstairs.

So yeah, he's kinda harmless but I suspect he might either be too excited, early dementia or slightly on the spectrum, or something else, given he's likely over 80 and talks for ages. Rent was very cheap for the area and my Japanese friend said that was suspicious. He also told me about the neighbors so I'm likely not the only one he talks to.

What do you recommend, and have you been in a similar situation?

EDIT: It has been three days and he came back ringing my door again this morning as I just got done showering, this time angrier because my bike fell down because of the wind and that I should have parked it more forward inside the mailbox area (which I avoided because it would be inconvenient for everyone trying to use the mailbox). I have tried ignoring him but he just stands out there and I have told him that I'm busy. I'm just going to document this and report it to the management company for now, but chances are slim that he'll move out since I've seen the inside of his house when he opened the door once and it's packed with stuff like he's been there forever and the company might not be able to kick him out.

by 500ar