My daughter is 14 months and she absolutely understands "no", "don't touch", "out of your mouth" etc. But she will look right at me with a smirk and do it anyways! In that case I remove her and redirect her to a different toy/area (and she throws a huge fit but doesn't go back to whatever it was she was doing that I asked her not to). They love to test their limits at this age and see what they can get away with! I say, just be consistent!
I also have a 12 month old and a 13 month in care and they both look at me if I say "no" and usually listen!