I'm 49 years ol and due to leave my current job in August 2015 after 30 years in the civil service
The job requires you to use your initiative, so please read the wealth of information already kindly posted on this site, by those of us who are already drivers. (Emphasis on the latter statement).
Much depends on your previous life experience, and also on your location. You have to reside somewhere that trainee drivers are recruited (think large urban areas), or be able to apply from the same
Register for vac alerts from TOC's.
Understand the skills required, and think how you can demonstrate them, from you work experience.
Previous time in the industry is NOT required, PROVIDED you have the skill set that a trainee driver needs, and that you are located somewhere that trainee drivers are recruited. If you don't have the above, the railway is still a very good place to work. Certainly consider other options.
Good Luck!