Funnily enough I have exactly the same problem.
My gmail address is firstnamesurnameh at gmail.com (I’ve had this since gmail first started) lately I keep getting emails clearly meant for someone else.
I was working out from the clues that the person concerned lived somewhere in Texas, has recently bought a new car, has applied for credit, has bought electrical goods with extended guarantees . . . Etc etc.
Eventually I got an email meant for him that showed somewhere in it that his email address is firstnameDOTsurname at gmail.com (which shows that either you can create an address the same as an existing gmail address but with a dot in it, or you can’t, but he thinks he did?)
Not sure if he ever gets mail meant for me . . . .