If the address was printed as your address on the envelopes (not handwritten) then you absolutely can write on the envelopes themselves "return to sender - subject not at this address" or if you know the exact address: "WRONG ADDRESS LISTED! CORRECT ADDRESS IS: 123 Street" and put them back in your mailbox. The postal carrier will pick them up and they'll eventually be returned to the issuing company or if they are feeling particularly generous, they'll deliver it to the guy if you wrote the correct addy on there, and it's on their way that day.
But if you don't mind talking to people (I do, so I do the above suggestion), I'd instead go directly to the neighbor and tell them that these are all incorrectly listing your address and that this may cause him grief in the future if his address is incorrectly listed in his credit reports and he needs to contact the companies and get it corrected. In the future, you can then mark them all "return to sender/wrong address" stuff since the guy was alerted to the fact that he's got incorrect addresses floating around out there and either he is accidentally/deliberately doing this on credit applications/forms (but there is no advantage to him for deliberately putting a slightly wrong address as it only complicates his credit history and looks like he can't fill out a form correctly so likely if he's the one doing it, it's sheer carelessness) OR it is the agencies he is applying to transposing numbers themselves (in which case, no big).
In any case, this isn't going to hurt or reflect on you at all. Address numbers get transposed all the time, he's never lived in your house and is no relation, and it's just going to show on his report that he's lived at YX address and XY address (and other variations likely). I've seen it on my own credit reports - an apartment number is correct, then it's one number off, and then they've left the apartment number off completely for on location. Human error in all its glory.
But on a side note, do check your credit reports at least every other year if you don't already. Highly unlikely this has anything at all to do with it, but they're free and it's a good thing to stay on top of for your financial health.