A little more detail on the age difference: I'll be 27 on Sunday, he's 45. He knows I have a boyfriend, it's not a secret. He once asked me out for drinks, I declined.
He does give me the creeps. He was nice at first, but then got clingy. He has a cool dog, which is how we met in the first place. I was walking my dog (who passed away in March) and he had his dog. He gave me his apartment key to hold on to in case he got locked out. I gave it back, but he returned it when he briefly went out of town. He asked if he could come by and pick it up, I said yes. He came by and tried to make an excuse as to why he should leave it here. He pretty much made an excuse to meet up, I insisted he take it. He also moved out of the complex 2 months ago and into a neighboring one. He used to live in the same building, not anymore, but still comes over. I do feel a little bad for him because I don't think he has a lot of friends here. I just wish he would meet friends his own age.
Even outside of the creepy situation, I was raised to not surprise anyone unless you know they're okay with it. Close family friends and family, maybe. I don't think showing up unannounced is the same interruption as calling. It's easier to not pick up a phone than pretend you're not home when they see your car in the carport. I wouldn't put it past him to look in my window (although I've never seen him do it).