Directed more at people in the know. Is there an age that's earmarked as a cut off point for potential new drivers?
I've always fancied driving but happy where I am for the next 3-4 years minimum where I'll then be 43
My particular group of trainees ranges from early 20s - mid 50s, average age late 30s.
Looking at other trainees at my depot, the greatest weighting is the range from early 30s - mid 40s. I can't imagine applying at 43 would pose you any problems at all. If anything it would be seen as a benefit in an industry where life experience and maturity are valued, perhaps more so than other careers.
Another point to consider is that "off the street" driver recruitment seems to be feast or famine. There are quite a few opportunities around at the moment with various TOCs. This has been the case for the last couple of years, but I remember a period prior to this where there was precious little out there for years on end. So, if you do fancy it, I would say apply sooner rather than later to benefit from the current boom.
Also, keep in mind the process can take two years or more from first application to start date.
Best of luck!