Q: IV for AES always 16 bytes

Playing with AES encryption and I want to ask what happens if we use the IV like a "Password", but it is chosen less 16 Bytes from the user :-/

From the examples:

//  Set the IV to a known value that will be used on both sides.
    //  (If desired, you could generate a random IV and protect it in the same
    //  way as the key...)
    //  The length of the IV for AES is always 16 bytes, regardless of the key size.
    crypt.SetEncodedIV("000102030405060708090A0B0C0D0E0F","hex");