More of a concern is has he had experience with such a large constrictor. I mean working with a snake since it was a baby and 'growing' together with it is a LOT different than buying a 20' snake that you meet for the first time. Unless you have lots of experience and not just blowing smoke to sound cool, i would start with a small one and like i said, 'grow' with it.
And also i hope you have a source for goats and pigs available as something that size is not going to be happy either a couple jumbo rats or a couple rabbits lol. Guy i know with i believe she is a 18' female feeds it goats and stuff but like i said, he has his own farm and raises wolves, breeds Black Roughneck monitors and has large constrictors so he has chickens and goats and very capable of meeting the snakes' needs.