My logic I think is pretty simple. A pilot hired at age 30 will top out at age 42, giving them 23 years at the top of the pay scale. Hire a 45 year old pilot, that pilot only rides the top of the pay scale for 8 years. A much cheaper employee to employ for the length of there career. Not only in pay, but vacation, sick time, etc. I agree Delta does not have to look for a replacement pilot for 35 years compared to 23. But at this current time replacement pilots are not hard to find. Longevity is what makes a pilot group expensive. If Delta hires all guys in there 30's pay roll is going to be expensive for a long time.