Ranger Batts do not do FID. I think there are many SOF missions that the Marines and Rangers do with junior troops. I would say FID and UW would be the exceptions I can think of right off the top of my head.
He acknowledged that - during our discussion we were trying to nail down at least the beginning of a concept on how to keep a force with specialized skills requiring extensive training and education young. The USMC will be conducting FID so there is a requirement for younger Marines to be trained for this mission. By UW, do you mean unconventional warfare?