The 757's are not 22 years old. The oldest (G-BPED) is 16 years old and the youngest (G-CPET) is only 9 years old. Info from airfleets.net
The 757's will be perfect for the all business class Europe-US flights that BA is planning. Fitted out as 2-2 with NGCW I would imagine you'd be looking at 50-60 seats in all and with the range to do a trans-atlantic which the A32X series lacks.