A.G.
My son (now almost 4years old) cut his first tooth at 4 months as well. It's in the realm of normal..although on the early side, at least that is what my family doctor told me. He had all his teeth except for molars by one year. When he was that little he really liked teething blakets, Munchkin makes them. As he got older I let him knaw on a frozen waffle. He loved it.
Good Luck and enjoy those cute first smiles with teeth.