Hello,

You can purchase those seats by calling in to Air China.

They charge $100 USD to reserve seating in the U.S. so not sure how many Euro's they will charge.

Even if you take a crappy middle seat for rows less than 50 , you still have to pay the same fee as you would to get a better economy seat.

They all become avail during check-in. CA cares less if it's a senior aged passenger.