I have to disagree with the idea that age is unimportant.
I personally find every type/role change harder than the last, and in training we always find that the young 18/19yr olds win the prizes despite generally very poor work ethic and partying a lot whilst the older (late 20s early 30s) guys have a far better work ethic but struggle.
I recently had the misfortune to be crewed with a very experienced aviator, who from his background must once have been an exceptional pilot who was frankly dangerous in terms of handling skills to the point where I was concerned about early onset altseimers (he was late 50s).
The simple fact is that whilst experience grows as you get older (to some degree. I'm not convinced that anybody is learning much from doing the same thing 1000 or 2000 times), the basic skill diminish with time. There is a reason why nobody fields 60yr old fighter pilots. I realise that these skills are vastly more important to the military, but they are still important to a lessor degree in all flying.
The older you are after a certain point, the harder you will find the training, and the more likely you are to give an airline expensive medical bills.
It sucks, and I am certainly past my best point on the curve, but that does not mean it is not true.