has at least a dozen "Senior First Officer's" on its A330 fleet younger than 25. Can't say I'd be too crash hot going from a 172 to an A330.
While I do see the point about better airlines having better training schemes, there's nothing preventing a mid twenty something from being an airline Captain (at one of the better airlines) if they're up to the job. Get them out of High School at 18, then a two year comprehensive training course and then 5/6 years as an FO will give them 4/5000hrs jet time, nothing stopping them from then progressing to the LH seat if they're up to the task. It has happened in Aus carriers in the past:
British Airways hands 21-year-old dream job as a pilot | Daily Mail Online