FYI, there is ONE group of cabin crew nowadays at Heathrow (and had been since late 2020), consisting of ex Mixed Fleet, ex Worldwide, ex Eurofleet, transferees from Gatwick, and brand new recruits (of all ages). All Heathrow crew work together on all aircraft on all routes, so it's nothing more than a fluke that you got "very young cabin crew" on all your PDX routes. Exactly the same crew work the JFK/JNB/HND/EDI etc flights.