You don't need to be that fit! After a couple of weeks of riding everyday you'll feeling pretty good and so already have a natural advantage over the guests.
It seems the only qualifications that you can get over here is the SMBLA, which definitely teaches some good stuff. However it's useless abroad seemingly in official eyes. Well worth doing. This involves needing to have an outdoor geared first aid course, which is at least 12 hours.
Additionally a sturdy bike and a leather scrotum help. The bike handling comes along very quickly with riding everyday. I guess good communication and people skills also…
Should have said that the SMBLA covers some mechanical skills, which are essential also.