I'll try to give you my perspective. I was a pilot for Netjets for over a decade, and left for the airlines because my career progression was non-existent. It took me over nine years just to move into the right seat of a slightly more comfortable airplane. I was on track to be a 15-year first officer, and when I finally upgraded, it would have been into the tiniest jet in the fleet (with no APU), most likely until at least age 60.
It was certainly a gamble moving to the bottom of a new seniority list, but after 10+ years, I was only 15% up the list at NJA, so I honestly didn't lose much ground in that respect. There's no retirement age. I believe at this point they have some 80-year-old PICs.
Anybody can use any base on that list; you're mostly airlining to/from your base. The jets aren't really "based" anywhere, and if you don't happen to pick up one at your home airport (it happens, but rarely), you'll get an airline tickets on each end of your work week. You'll keep the frequent-flier miles (and hotel points), which is nice. There's no ability to jumpseat, so that's your only option for free flying.
Company-wide. Seniority within your fleet/seat applies for vacations and schedules.
More or less. For 2016, it was 9% for me. Some years was as low as 6%.
The others are the "Crew Choice" (CC) schedules, the CC52, CC60, CC72, and CC76. Those refer to how many workdays you'll work within the 4-month bid cycle. The CC72, for example, would average to 18 days a month, which can go up or down by 2 days at scheduling's sole discretion, as long as the total doesn't exceed 72 days in 4 months. So you might work 16, 20, 20, and 16 days in a cycle.
The specific workdays are created as a monthly schedule bid using a preferential bid system, and scheduling will publish your schedule by the 15th of the month prior. Seniority plays very little role in the PBS, and in most cases you'll only be able to get one preference (e.g., a single day off, or want to work holidays) with any degree of success.
If you agree to 8-day tour lengths, there's a 3% pay override for the bid period.
There are limits. I don't have the CBA in front of me, but if memory serves, the CC52 (lowest-working) schedule is limited to 10% of the pilots in a fleet/seat, as are the schedules with a maximum of 5-day tours. Also, the schedules with 5-day and 6-day tours are limited to a smaller subset of the bases that have significant airline service and a large amount of Netjets customer flights.
One thing you
can't bid on is the particular trips, which makes sense because everything is on-demand. You never know where you'll end up, so you'll bring warm and cold weather clothing on every trip.
There are a lot of ancillary tasks in addition to the flying, including loading/unloading luggage, restocking the snacks and drinks, cleaning up after a flight, removing
all the liquids every night (and replacing them in the morning) when a plane is parked in freezing weather, and so on. There's a little help from the FBOs, but for the most part it's just a two man show to keep the jet in passenger-ready condition.
When you're on duty at the airport, catered crew meals are provided. Quality varies wildly and is usually mediocre, but it's convenient and fully paid by the company in addition to per diem.
It's a fatiguing, hard job on many days. Circadian shifts are commonplace -- you may report at 10am on your first day, 4am your second, 10pm your third, and be expected to put in a 14-hour day no matter when you start. There's a fatigue policy that most pilots are very familiar with, because you'll be scheduled until you cry uncle with it.
Days are frequently augmented with hours of "hot spare" or "tentative" duty where you're trapped at the airport in case of another assignment. If your scheduled day of flying is less than 10 hours, you're all but
guaranteed to have one of these assignments tacked on to bring you up to 12 hours. (More than 12 pays overtime, so that's usually where it stops if nothing comes up.)
It's not a bad job by any means, but it's a lot of work for not a lot of money, comparatively speaking. I think airlines are a far better bet from a career earnings and sanity standpoint, but they aren't for everybody. I wish your friend's son luck in his career!