They wouldn't be able to turn you down on the basis of your age alone. I have a friend in her early forties who's just qualified. However, you would need to show that you have (or would be able to develop) the required stamina, fitness, intellectual capacity and attitude for the work (which can be at degree standard, and that's
hard work).
It seems that the 5 GCSE's requirement isn't written in stone:
http://www.nhscareers.nhs.uk/details/Default.a spx?Id=125
Could be you have other qualifications or experience that could be taken in lieu of this. If you're not already, then finding work as a health care assistant for the NHS or a reputable organisation could be a good start, because then you'll have access to stuff like NVQ programmes that can be used to get you onto the nursing training ladder, plus gaining experience as you go.