Oh yeah, that's a rooster! Check his feet and make sure there is not any type of infection within the folds of his toes. Make sure your perches are clean and mite free and provide a perch that is flat instead of round. I have discovered that older chickens tend to appreciate a large flat perch- a 2 x 4 flat side up works fine. Examine him closely and be mindful of swollen hocks or possible fractured pelvis. Does he keep both wings close to his body? A bird who can't positions one or both wings may have arthritis in the neck or shoulder area. Otherwise this guy just might have a strong maternal instinct. I have a rooster that likes to sit in the nest box on special occasions (according to him) but he usually sits on the nest during the day to assist the hen during her 'labor'. Also your rooster could be kicking the hens off the nest just to prove that he is the boss.