I agree with PP on his comments when I started flying there were better pilots than me both older and younger. There has always been many companies who liked to recruit older pilots as they were more likely to stay in the company and put in a good few years LH seat where many younger pilots would only see it as a stepping stone.
It is probably easiest to teach students to fly at 17 but airlines aren't that keen as they lack other important traits which they will gain with age.