I don’t know if this information is of any use but purely as a point of interest, in the last seven years, recruitment (and the bmi takeover) has been such that just over one third of BA pilots today have been in the company for seven years or less. If you’d joined straight after the takeover, this is where you could be today in approximate percentage terms from the top of each list:
Gatwick Airbus: Captain 65%, FO <5%
Heathrow Airbus: Captain 95%, FO 10-15%
747 FO 50-55%
777 FO 65-70%
787 FO 60-65%
A380 FO 80-85%
As the A350 is a new, and growing, fleet no meaningful data will be available for quite some time. This information is a statistical snapshot and should not be taken to mean that if you join now, this is what you can achieve in seven years.