I am forty and I am just over half way through my training course with a fairly well known training provider. Having been out of a learning environment for well over 20 years the initial groundschool was tough, but with hard work I came through with mid 90's average marks. Not as good as some but better than others. The flying itself is intensive but enjoyable. I spent a lot of time prior to the course looking at how instruments work etc and this has helped a fair amount. It is too early to make a judgement about my flying ability but my gut feeling is that I will be just above average.
All of the above won't make a huge difference with an prospective employer who has 'training risk' issues with older applicants but at least demostrates to other employers that if I am good enough, I am young enough.