sea walk is not allowed for elderly especially who had operations. They charge 1500-2000 thai baht per person for 30 min. They take you to ferry parked in sea via speed boat. You can change your clothes if you want. And they provide you baskets to put your belongings things like bag, wallet, mobile phones etc.
Then they guide you what is sea walk and how will things work and most important they show you that particular sign language for sea walk, because when we inside the sea we can't hear anything except the googling sound of water.