He has a crazy imagination and can make many things up. His father biologically hasn't been around much when he was younger and his mother married another man, who Dill said was the reason he ran away. Since he felt that they were having far more fun without him around. He felt he was unneeded.
Dill is one year older than Scout and three years younger than Jem, as was told to us in the first chapter. Although Scout confuses him to be younger than even her when she first met him.
He is described as rather short for even his young age.