Oliver Obsessions

My 2 1/2 year old is obsessed with the stairs in our apartment. He likes to go up and down , up and down, all day long. He goes up the stairs really good ,but then he likes to stand at the edge of the top stair. This makes me very nervous. His other obsessions are letters and shapes. He can't get enough of them. He knows all the letters and their sounds and can sing the ABC song. His favorite letter is W. He likes to turn it around and say "W,M,W,M. He is our very silly boy.