Of the 9 planes in this seat configuration only 3 came from Wizz, the others were from fellow OneWorld airline TAM (Brazil). They are identical A320s to others in the BA fleet, they aren't the oldest BA have, even the seats now fitted are the same as most of the other BA A320s. The only real difference is the seating layout, with what is effectively an extra half-row at the front where a wardrobe is fitted on new-to-BA aircraft.
Ten planes were originally expected, and went through an extensive refurb process during which they were BA-ised. When they were stripped for refurb BA engineers discovered one had problems and this was rejected, which is why there are only 9 in service. A replacement for the 10th plane is expected in time for summer.