Been to Philmont as adult advisor twice, 1996 and 2002. Absolutely wonderful experience. First trek was in the north, and included going into the Valle Vidal of the Kit Carson National Forest. Second trek was in center of Philmont. All beautiful country.
Adults should lose weight, get in shape, and lose more weight. 11 days of backpacking and sleeping on the ground for 10 consecutive nights is fairly demanding.
We spent a lot of time preparing our groups of Scouts. We talked about a lot of things, got together for training hikes, and spent some weekends camping. The goals of the advisors were to have the Scouts ready to take charge once we got to Philmont, and the adults wanted to be able to step back, let the groups be lead by the crewleader picked by the Scouts, offer advice when asked, and we planned to intervene only if health and/or safety were involved. We were successful in meeting our goals.
A Philmont trek is demanding, but provides a great opportunity for 14-17 year old Scouts to earn some self-esteem that lasts a lifetime.