I don't believe your ever too old to start..
It looks like airlines are now starting to lift the age ban on applications, BAFPP, Gen easy jet, Virgin MPL all have no upper age limit. From talking to people and from looking at the Facebook profiles of the schools, it looks like there is a large spread of experience in new cadets. From someone on the BAFPP last year, he said there lots of people in their 40's applying.
But that said, you'll have to think long and hard about if it's worth it (financially and emotionally). But it looks like everyones on a flat playing field now. You've got to be in to to win it though.