What age should a baby hold its head up?

it can depend on the baby, my sis has a 2 month old baby girl, she seems so clever, shes been trying to hold her head up since she was about 3wks old! She may be able to do this but she cant support her head for too long, let him/her hold her head up themself if they can, just be ready to take the pressure of the baby when they cant hold their head up.