Back to the subject at hand:

Here are some numbers from the APC profile page.

Retirements from 2019-2028:

AA - 8,302
DL - 6,483
UA - 5,163
Total - 19,948

That's just mandatory retirements. Throw in lost medicals, early retirements, and deaths.

Basically 20,000 pilots lost just at the Big 3. Throw in the competition for pilots from FDX, UPS and the LCC's, and it's gonna be interesting.