Oh hun, big hugs You've worked some of it out yourself. It is so hard not to compare our kids to others, but we do. It's some sort of stupid natural in built thing.

FWIW, my niece did the headbutting floor thing and she was born at 41+3 at 9lbs. My DD has bitten herself in frustration and she was born at 39+5, 8lbs. The behaviour scared my sister and me respectively, but we handled it the same - ignored, or tried to diffuse. My DD was older when she tried to bite herself - I gently held her arm and said "Don't do that. Are you frustrated? Tell mummy you are frustrated, use your words." But she is 3.5, so it is a bit different.

When they were younger, and my DS is 20mths and still hits things, I say "No! Gentle! Keep your hands to yourself!" which seems to work. I can reason with DD now she is older.

FWI also W, DD had a massive word explosion around 18mths and was using sentences by 2. There are so many ranges of normal!!