There is unpaid leave available on several fleets this summer. Mostly for F/Os.
According to the Balpa age demo-graphic figures there is a bit of a bulge of retirements forecast around 2020.
However, a large number of the top 1500 pilots are aged around 50. The real floodgates open in about 15-20 years, but who knows what will be left of BA by then.....
All this assumes every pilot working to 65 and no part time or expansion.