Tough one - the job might give you some useful contacts, although just meeting people isn't really good enough you have to get to know then and be likeable enough for them to do you favours. It will give you some valuable "real life" experience with people in a professional context though and maybe make you better at managing your relationships with colleagues when you get your airline job. At 19, I needed that kind of experience.
On the other hand, the job market is still strong and if you delay by a year things might be very different when you finish training.
In summary, if you're a particulary mature 19 year old and you have no problems dealing with people then I wouldn't bother taking the job as it won't really teach you much, but if you think you need to develop stronger interpersonal skills (always a hard one to judge yourself!) then I would take it as it might get you off to a stronger start in the airlines..
Good luck though - I wish I was 19 again!