747 PE Bubble Exit Row Seats

Hi
Does anyone know how VS allocate the exit row seats in PE for those sitting in the bubble (I think the seats are 75AC/HK)?
Are there rules regarding being fit/able to operate the emergency exit doors? I believe the exits are only used for an emergency land exit, and not in case of landing on water.
The reason I ask is that in the last 3 of my 4 flights in the bubble, the seats have been occupied by elderly passengers. One couple were in their 70s, and one of the passengers had recently had a hip replacement.
Does anyone know how VS allocate the exit row seats in PE for those sitting in the bubble (I think the seats are 75AC/HK)?
Are there rules regarding being fit/able to operate the emergency exit doors? I believe the exits are only used for an emergency land exit, and not in case of landing on water.
The reason I ask is that in the last 3 of my 4 flights in the bubble, the seats have been occupied by elderly passengers. One couple were in their 70s, and one of the passengers had recently had a hip replacement.