I would suggest that if BA is the company you want to work for a-Ricky-town and if you meet their minimum requirements then apply as soon as possible. At 31 I wouldn't waste any time and I certainly wouldn't try and second guess their future needs!
The BA recruitment is very black and white. If you tick the right boxes by way of your minimum requirements, essay answers on your application and then the subsequent recruitment process then you'll be given a shot.
My advice to anyone looking to join a large airline would be to apply as soon as possible in order of getting on that seniority list sooner rather than later as seniority is key in the path of your future career within the large airlines.