What's wrong with being 40 when you start training?
Nothing whatsoever. Just don't be too surprised if after you qualify you find yourself unemployed, £70k lighter and trying to return to your previous line of work. At the moment there are pilots who tick all the boxes for employability stacking shelves and flipping burgers. You'd be a brave man to embark on professional training at the moment but if you wish to roll the dice it's your call.
Good luck!