P1 Forever
I can only speak from my experience, but I do not think you would be disadvantaged with regards Britannia, but, and this is the big but, if you have 4500hrs flying turbo-props at that age the question that springs to mind is "why has it taken you so long to apply for jet jobs, aren't you ambitious enough?"
That would be what I would ask if I were interviewing. Get a good answer lined up to explain why would be my advice. Remember you are up against an incredible amount of competition for the few jobs on offer. It's not good enough to convince yourself that you fit the bill, you have to convince them, who may not view you as desireable as you may think you are. Assuming you have 3000hrs on a turbo-prop after say instructing to 1500hrs that means you have spent somewhere in the region of 4 to 5 years flying turbo-props. 5 years ago with turbo-prop experience you (not you particularly) could have got a jet job. So it begs the inevitable question.
However, as far as age commensurate with experience goes you would not be in too bad a position. It's all common sense really and a case of doing the homework about the company that you want to work for. For instance, when I joined jmc I was at their 'upper' desireable age limit due to their age demograph; they already had a bulge in pilots who were in the age bracket just above 35, hence they were avoiding getting any more in that bracket.
So it comes down to doing your research and targetting the airlines where you have a chance of employment. No airline will ever turn round to you at application stage and tell you that you don't fit their age profile, because they can't, it's against the law.
Best of luck with it, do your homework guys!
PP