Old thread, but still having the issue. I've already done the "force stop/clear contacts storage" thing, which deleted every contact on my phone. Also did the same thing with the gmail app (force stop/clear data/cache). I also went into gmail on my computer and cleared out everything I didn't want on "other contacts". I've also tried all the things suggested in this thread. Basically, I think I've tried every fix I've read about online, and I still have old/bad autofill addresses coming up in gmail.
If it matters, I'm using a 2nd gen Moto X with android 5.0 running. I think this is a gmail app issue, and not a phone/android issue, but I can't figure out how to get rid of these annoying autofill addresses!!!
Oh, and BTW, the funny part is that none of these autofill addresses show up on gmail if I'm using my computer. Only on my phone.