Baby school

I wonder at what age a baby can start to learn 'no' and 'gentle'?

Baby has always been an arm flapper, but she's getting better with her hands. She's reaching for things and grabbing for things - she grabs out at our noses and mouths, and grabs the husbands hair when he raspberries her belly.

I am trying to teach her to be gentle for this sort of stuff, but how? We did puppy school with our dogs, so I have an idea with them, but I have the feeling this might be just a little different....!