The problem with joining at a later age in BA is that the demographics work against you. There are approx. 100 pilots due to reach 65 in the next 5 years, followed by around 400 pilots in the 5 years after that.
That is out of about 3500 pilots.
Assuming that you are looking for a long haul command, I'm guessing that it would take a new joiner around 20 years to achieve it.
That together with the upcoming changes in pension LTA's, I'm guessing an awful lot of people are sitting there crunching the numbers.