Anyone can use twofish without restrictions, as its makers did not patent it and made it available to the public. In fact, it is one of a few ciphers included in the OpenPGP standard (RFC 4880), the most widely used email encryption standard today.
Schneier isn’t the only one responsible for developing twofish, several other cryptographers who made up the so-called “extended Twofish team” helped out. They are John Kelsey, Doug Whiting, David Wagner, Chris Hall, and Niels Ferguson.