life
If you are concerned you should ask your HV. It would be perfectly reasonable to ask for a proper check if a baby isnt weight bearing at 11mths.
I am not saying there is a problem so please dont worry.
But personally I would insist on a check up.
My DS2 had odd muscle tone and wouldnt weight bear at 9mths ish. I was concerned about CP because of his history. The physio was also worried.
As it happened it seemed to resolve its self (with a bit of physio) and he turned out not to have CP. His gross motor development is now perfectly normal.
Ask HV or CP for a ref to the Child Development Team.