checkxp - I'd second tom775257's advice whole-heartedly; sensible. No-one knows when the upturn would come but you can start training at that point and not miss it. Take the grad job you have lined up; build life experience, a fallback career and some capital
.
As regards worrying about loyalty to that company; I've both been through a grad training scheme and recruited for them. Your concern is honorable and your company may not be like this ... but many companies simply see their big grad intakes as 'cannon-fodder' because they know that most will leave after a few years. Whether it's the accountancy firms, engineering, banking or law, it seemed to work the same way - there are only a limited number of higher jobs to go for when you finish the scheme and until you're performing on the scheme no-one really knows who will be the stars. People leave, people swap companies etc and no-one feels 'slighted' by it; it's just the reality of the job market these days.
Grogalong - apologies for the threadcreep. Back to the point & to try to answer your question. I got a job a few years ago on a 'cadet' or 'tagged' scheme with a UK carrier when a bit older than most. In the selections I undertook (5 airlines, mainly UK) I never saw anyone over early 30s get onto the scheme. My age was always something I had to convince the airline interviewers was not a problem.
I don't know about the other routes, other than that there are success stories out there from people your age but that now is a horrendously bad time to be trying to get in
.
Best of luck, BM