PCGU... Bottom line is that if you do get a job as an ATCA at anywhere other than a NATS unit you might (note I said "might") be just a "general" assistant doing a variety of jobs on not very good pay.
In NATS, many ATSA positions carry a great deal of responsibility and they pay well but this may not be the case in the outside world. If you want to sit around answering the phone, writing out flight progress strips, logging aircraft movements and making tea then you may find the job attractive.
Advancing years will generally be against you if you are ever accepted for ATCO training. I read on PpruNe today that Eurocontrol do not accept ATCO trainees over age 24. I don't think a similar rule applies here because of government legislation. If you start young you can grow up with the job and still be very efficient later in life. However, starting from square 1 with no previous experience at age 30 may prove difficult but, of course, there are always the exceptions to the rule.
I appreciate what you are saying about your background, but do you really know much about air traffic control? I suspect that adverts for positions which do not require any background are really adverts for tea boys!!
Good luck