I agree that SWA gotta slow down at some point, but than I'd never have guessed (15 years ago) that SWA would even try to make a presence on the East coast; so much for my crystal ball!
While I wouldn't want to be 45 looking to get in at a regional, many pilots at FDX have started at 40 something and are happy with (what little) career they will have before retirement. Agreed, it would be different at a "real" airline, still you got to do what makes you happy.
Older pilots should look carefully at the retirements (or lack there of) of their future/present employer. Considerations of upgrade due to retirements are one area were an older vs younger pilot should make differing career decision's based on the demographics of their airline. SWA, would, on the face of it, be a less desirable choice than, say, CAL due to retirements in the near to medium time period.