I sat next to a dozen or so bright young things (boys and girls) on way to IAH for training. Nice to see new blood coming in.

I have had a few on pmUA at the beginning of the year.

Exactly, PMCO has lots of new metal coming 737s and 787s from before the merger, while PMUA had been shirking for the last 6 years.

As far as I know CO has always had these familiarization flights for new crew.

Also correct that sUA is at the same time offering buy out, so the sum total should be a younger fresher work group in the end.

Over the years, I've enjoyed a number of flights with trainee FAs. IME the women were given a dress code that said solid-color pastel dresses, stockings, and heels (PanAm TV show?) and classic (rather conservative) business suits for men. One flight had almost twenty of the trainees on a narrow body, IIRC a KLM 737; they must have been observers. They all are assigned regular seats because apparently only official trained FAs can take the jump seats. I find it fun to watch the youthful eagerness and enthusiasm, but perhaps others object to the training being inflicted on paying passengers. It can slow the drinks service as well as meals, but I like to encourage then nevertheless as they all are on their best behavior throughout the flight.

Two, no, three^

In Dec 2010 we had 1 female trainee and 1 male trainee on a flight from IAH-SJD. The passengers all thanked the trainees as we de-planed. They did a great job but haven't had any flights since then with new FAs.