Here is a touchstone of typical through the years:
AA has 15,000 pilots, +/-
Assume every pilot gets hired at age 30 (probably actual average will be a bit higher)
Assume no early outs for medical, etc. That would require hiring.
Assume no growth, at all. That would require hiring.
Assume mandatory retirement remains at 65.
Assume 2 pilots are required, and relief on long hauls stay the same.
If age distribution was uniform (I know it isn’t):
15,000 total pilots / (age 65 - age 30) = 428 retirements per year on average.
That gives a bit of a touchstone for these numbers. Typically the retirements will be more, due to conservative assumptions. Some years less, some years more.